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![Steve Capper](/assets/img/avatar_default.png)
This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1032 lines
30 KiB
C
1032 lines
30 KiB
C
#include <linux/kernel.h>
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#include <linux/errno.h>
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#include <linux/err.h>
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#include <linux/spinlock.h>
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#include <linux/hugetlb.h>
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#include <linux/mm.h>
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#include <linux/pagemap.h>
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#include <linux/rmap.h>
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#include <linux/swap.h>
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#include <linux/swapops.h>
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#include <linux/sched.h>
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#include <linux/rwsem.h>
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#include <asm/pgtable.h>
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#include "internal.h"
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static struct page *no_page_table(struct vm_area_struct *vma,
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unsigned int flags)
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{
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/*
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* When core dumping an enormous anonymous area that nobody
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* has touched so far, we don't want to allocate unnecessary pages or
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* page tables. Return error instead of NULL to skip handle_mm_fault,
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* then get_dump_page() will return NULL to leave a hole in the dump.
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* But we can only make this optimization where a hole would surely
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* be zero-filled if handle_mm_fault() actually did handle it.
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*/
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if ((flags & FOLL_DUMP) && (!vma->vm_ops || !vma->vm_ops->fault))
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return ERR_PTR(-EFAULT);
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return NULL;
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}
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static struct page *follow_page_pte(struct vm_area_struct *vma,
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unsigned long address, pmd_t *pmd, unsigned int flags)
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{
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struct mm_struct *mm = vma->vm_mm;
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struct page *page;
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spinlock_t *ptl;
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pte_t *ptep, pte;
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retry:
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if (unlikely(pmd_bad(*pmd)))
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return no_page_table(vma, flags);
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ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
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pte = *ptep;
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if (!pte_present(pte)) {
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swp_entry_t entry;
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/*
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* KSM's break_ksm() relies upon recognizing a ksm page
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* even while it is being migrated, so for that case we
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* need migration_entry_wait().
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*/
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if (likely(!(flags & FOLL_MIGRATION)))
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goto no_page;
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if (pte_none(pte) || pte_file(pte))
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goto no_page;
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entry = pte_to_swp_entry(pte);
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if (!is_migration_entry(entry))
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goto no_page;
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pte_unmap_unlock(ptep, ptl);
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migration_entry_wait(mm, pmd, address);
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goto retry;
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}
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if ((flags & FOLL_NUMA) && pte_numa(pte))
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goto no_page;
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if ((flags & FOLL_WRITE) && !pte_write(pte)) {
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pte_unmap_unlock(ptep, ptl);
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return NULL;
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}
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page = vm_normal_page(vma, address, pte);
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if (unlikely(!page)) {
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if ((flags & FOLL_DUMP) ||
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!is_zero_pfn(pte_pfn(pte)))
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goto bad_page;
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page = pte_page(pte);
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}
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if (flags & FOLL_GET)
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get_page_foll(page);
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if (flags & FOLL_TOUCH) {
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if ((flags & FOLL_WRITE) &&
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!pte_dirty(pte) && !PageDirty(page))
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set_page_dirty(page);
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/*
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* pte_mkyoung() would be more correct here, but atomic care
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* is needed to avoid losing the dirty bit: it is easier to use
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* mark_page_accessed().
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*/
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mark_page_accessed(page);
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}
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if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
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/*
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* The preliminary mapping check is mainly to avoid the
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* pointless overhead of lock_page on the ZERO_PAGE
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* which might bounce very badly if there is contention.
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*
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* If the page is already locked, we don't need to
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* handle it now - vmscan will handle it later if and
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* when it attempts to reclaim the page.
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*/
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if (page->mapping && trylock_page(page)) {
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lru_add_drain(); /* push cached pages to LRU */
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/*
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* Because we lock page here, and migration is
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* blocked by the pte's page reference, and we
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* know the page is still mapped, we don't even
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* need to check for file-cache page truncation.
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*/
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mlock_vma_page(page);
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unlock_page(page);
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}
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}
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pte_unmap_unlock(ptep, ptl);
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return page;
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bad_page:
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pte_unmap_unlock(ptep, ptl);
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return ERR_PTR(-EFAULT);
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no_page:
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pte_unmap_unlock(ptep, ptl);
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if (!pte_none(pte))
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return NULL;
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return no_page_table(vma, flags);
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}
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/**
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* follow_page_mask - look up a page descriptor from a user-virtual address
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* @vma: vm_area_struct mapping @address
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* @address: virtual address to look up
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* @flags: flags modifying lookup behaviour
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* @page_mask: on output, *page_mask is set according to the size of the page
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*
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* @flags can have FOLL_ flags set, defined in <linux/mm.h>
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*
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* Returns the mapped (struct page *), %NULL if no mapping exists, or
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* an error pointer if there is a mapping to something not represented
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* by a page descriptor (see also vm_normal_page()).
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*/
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struct page *follow_page_mask(struct vm_area_struct *vma,
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unsigned long address, unsigned int flags,
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unsigned int *page_mask)
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{
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pgd_t *pgd;
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pud_t *pud;
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pmd_t *pmd;
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spinlock_t *ptl;
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struct page *page;
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struct mm_struct *mm = vma->vm_mm;
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*page_mask = 0;
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page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
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if (!IS_ERR(page)) {
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BUG_ON(flags & FOLL_GET);
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return page;
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}
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pgd = pgd_offset(mm, address);
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if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
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return no_page_table(vma, flags);
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pud = pud_offset(pgd, address);
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if (pud_none(*pud))
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return no_page_table(vma, flags);
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if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
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if (flags & FOLL_GET)
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return NULL;
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page = follow_huge_pud(mm, address, pud, flags & FOLL_WRITE);
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return page;
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}
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if (unlikely(pud_bad(*pud)))
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return no_page_table(vma, flags);
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pmd = pmd_offset(pud, address);
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if (pmd_none(*pmd))
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return no_page_table(vma, flags);
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if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
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page = follow_huge_pmd(mm, address, pmd, flags & FOLL_WRITE);
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if (flags & FOLL_GET) {
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/*
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* Refcount on tail pages are not well-defined and
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* shouldn't be taken. The caller should handle a NULL
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* return when trying to follow tail pages.
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*/
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if (PageHead(page))
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get_page(page);
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else
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page = NULL;
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}
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return page;
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}
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if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
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return no_page_table(vma, flags);
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if (pmd_trans_huge(*pmd)) {
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if (flags & FOLL_SPLIT) {
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split_huge_page_pmd(vma, address, pmd);
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return follow_page_pte(vma, address, pmd, flags);
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}
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ptl = pmd_lock(mm, pmd);
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if (likely(pmd_trans_huge(*pmd))) {
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if (unlikely(pmd_trans_splitting(*pmd))) {
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spin_unlock(ptl);
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wait_split_huge_page(vma->anon_vma, pmd);
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} else {
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page = follow_trans_huge_pmd(vma, address,
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pmd, flags);
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spin_unlock(ptl);
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*page_mask = HPAGE_PMD_NR - 1;
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return page;
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}
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} else
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spin_unlock(ptl);
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}
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return follow_page_pte(vma, address, pmd, flags);
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}
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static int get_gate_page(struct mm_struct *mm, unsigned long address,
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unsigned int gup_flags, struct vm_area_struct **vma,
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struct page **page)
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{
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pgd_t *pgd;
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pud_t *pud;
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pmd_t *pmd;
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pte_t *pte;
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int ret = -EFAULT;
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/* user gate pages are read-only */
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if (gup_flags & FOLL_WRITE)
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return -EFAULT;
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if (address > TASK_SIZE)
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pgd = pgd_offset_k(address);
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else
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pgd = pgd_offset_gate(mm, address);
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BUG_ON(pgd_none(*pgd));
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pud = pud_offset(pgd, address);
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BUG_ON(pud_none(*pud));
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pmd = pmd_offset(pud, address);
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if (pmd_none(*pmd))
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return -EFAULT;
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VM_BUG_ON(pmd_trans_huge(*pmd));
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pte = pte_offset_map(pmd, address);
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if (pte_none(*pte))
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goto unmap;
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*vma = get_gate_vma(mm);
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if (!page)
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goto out;
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*page = vm_normal_page(*vma, address, *pte);
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if (!*page) {
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if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(*pte)))
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goto unmap;
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*page = pte_page(*pte);
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}
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get_page(*page);
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out:
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ret = 0;
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unmap:
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pte_unmap(pte);
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return ret;
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}
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/*
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* mmap_sem must be held on entry. If @nonblocking != NULL and
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* *@flags does not include FOLL_NOWAIT, the mmap_sem may be released.
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* If it is, *@nonblocking will be set to 0 and -EBUSY returned.
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*/
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static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
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unsigned long address, unsigned int *flags, int *nonblocking)
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{
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struct mm_struct *mm = vma->vm_mm;
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unsigned int fault_flags = 0;
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int ret;
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/* For mlock, just skip the stack guard page. */
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if ((*flags & FOLL_MLOCK) &&
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(stack_guard_page_start(vma, address) ||
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stack_guard_page_end(vma, address + PAGE_SIZE)))
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return -ENOENT;
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if (*flags & FOLL_WRITE)
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fault_flags |= FAULT_FLAG_WRITE;
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if (nonblocking)
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fault_flags |= FAULT_FLAG_ALLOW_RETRY;
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if (*flags & FOLL_NOWAIT)
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fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
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if (*flags & FOLL_TRIED) {
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VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
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fault_flags |= FAULT_FLAG_TRIED;
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}
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ret = handle_mm_fault(mm, vma, address, fault_flags);
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if (ret & VM_FAULT_ERROR) {
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if (ret & VM_FAULT_OOM)
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return -ENOMEM;
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if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
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return *flags & FOLL_HWPOISON ? -EHWPOISON : -EFAULT;
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if (ret & VM_FAULT_SIGBUS)
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return -EFAULT;
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BUG();
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}
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if (tsk) {
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if (ret & VM_FAULT_MAJOR)
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tsk->maj_flt++;
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else
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tsk->min_flt++;
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}
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if (ret & VM_FAULT_RETRY) {
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if (nonblocking)
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*nonblocking = 0;
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return -EBUSY;
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}
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/*
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* The VM_FAULT_WRITE bit tells us that do_wp_page has broken COW when
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* necessary, even if maybe_mkwrite decided not to set pte_write. We
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* can thus safely do subsequent page lookups as if they were reads.
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* But only do so when looping for pte_write is futile: in some cases
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* userspace may also be wanting to write to the gotten user page,
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* which a read fault here might prevent (a readonly page might get
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* reCOWed by userspace write).
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*/
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if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
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*flags &= ~FOLL_WRITE;
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return 0;
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}
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static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
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{
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vm_flags_t vm_flags = vma->vm_flags;
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if (vm_flags & (VM_IO | VM_PFNMAP))
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return -EFAULT;
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if (gup_flags & FOLL_WRITE) {
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if (!(vm_flags & VM_WRITE)) {
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if (!(gup_flags & FOLL_FORCE))
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return -EFAULT;
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/*
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* We used to let the write,force case do COW in a
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* VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
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* set a breakpoint in a read-only mapping of an
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* executable, without corrupting the file (yet only
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* when that file had been opened for writing!).
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* Anon pages in shared mappings are surprising: now
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* just reject it.
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*/
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if (!is_cow_mapping(vm_flags)) {
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WARN_ON_ONCE(vm_flags & VM_MAYWRITE);
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return -EFAULT;
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}
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}
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} else if (!(vm_flags & VM_READ)) {
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if (!(gup_flags & FOLL_FORCE))
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return -EFAULT;
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/*
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* Is there actually any vma we can reach here which does not
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* have VM_MAYREAD set?
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*/
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if (!(vm_flags & VM_MAYREAD))
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return -EFAULT;
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}
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return 0;
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}
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/**
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* __get_user_pages() - pin user pages in memory
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* @tsk: task_struct of target task
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* @mm: mm_struct of target mm
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* @start: starting user address
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* @nr_pages: number of pages from start to pin
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* @gup_flags: flags modifying pin behaviour
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* @pages: array that receives pointers to the pages pinned.
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* Should be at least nr_pages long. Or NULL, if caller
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* only intends to ensure the pages are faulted in.
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* @vmas: array of pointers to vmas corresponding to each page.
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* Or NULL if the caller does not require them.
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* @nonblocking: whether waiting for disk IO or mmap_sem contention
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*
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* Returns number of pages pinned. This may be fewer than the number
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* requested. If nr_pages is 0 or negative, returns 0. If no pages
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* were pinned, returns -errno. Each page returned must be released
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* with a put_page() call when it is finished with. vmas will only
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* remain valid while mmap_sem is held.
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*
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* Must be called with mmap_sem held. It may be released. See below.
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*
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* __get_user_pages walks a process's page tables and takes a reference to
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* each struct page that each user address corresponds to at a given
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* instant. That is, it takes the page that would be accessed if a user
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* thread accesses the given user virtual address at that instant.
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*
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* This does not guarantee that the page exists in the user mappings when
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* __get_user_pages returns, and there may even be a completely different
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* page there in some cases (eg. if mmapped pagecache has been invalidated
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* and subsequently re faulted). However it does guarantee that the page
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* won't be freed completely. And mostly callers simply care that the page
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* contains data that was valid *at some point in time*. Typically, an IO
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* or similar operation cannot guarantee anything stronger anyway because
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* locks can't be held over the syscall boundary.
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*
|
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* If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
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* the page is written to, set_page_dirty (or set_page_dirty_lock, as
|
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* appropriate) must be called after the page is finished with, and
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* before put_page is called.
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*
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* If @nonblocking != NULL, __get_user_pages will not wait for disk IO
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* or mmap_sem contention, and if waiting is needed to pin all pages,
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* *@nonblocking will be set to 0. Further, if @gup_flags does not
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* include FOLL_NOWAIT, the mmap_sem will be released via up_read() in
|
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* this case.
|
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*
|
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* A caller using such a combination of @nonblocking and @gup_flags
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* must therefore hold the mmap_sem for reading only, and recognize
|
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* when it's been released. Otherwise, it must be held for either
|
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* reading or writing and will not be released.
|
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*
|
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* In most cases, get_user_pages or get_user_pages_fast should be used
|
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* instead of __get_user_pages. __get_user_pages should be used only if
|
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* you need some special @gup_flags.
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*/
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long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
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unsigned long start, unsigned long nr_pages,
|
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unsigned int gup_flags, struct page **pages,
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struct vm_area_struct **vmas, int *nonblocking)
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|
{
|
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long i = 0;
|
|
unsigned int page_mask;
|
|
struct vm_area_struct *vma = NULL;
|
|
|
|
if (!nr_pages)
|
|
return 0;
|
|
|
|
VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
|
|
|
|
/*
|
|
* If FOLL_FORCE is set then do not force a full fault as the hinting
|
|
* fault information is unrelated to the reference behaviour of a task
|
|
* using the address space
|
|
*/
|
|
if (!(gup_flags & FOLL_FORCE))
|
|
gup_flags |= FOLL_NUMA;
|
|
|
|
do {
|
|
struct page *page;
|
|
unsigned int foll_flags = gup_flags;
|
|
unsigned int page_increm;
|
|
|
|
/* first iteration or cross vma bound */
|
|
if (!vma || start >= vma->vm_end) {
|
|
vma = find_extend_vma(mm, start);
|
|
if (!vma && in_gate_area(mm, start)) {
|
|
int ret;
|
|
ret = get_gate_page(mm, start & PAGE_MASK,
|
|
gup_flags, &vma,
|
|
pages ? &pages[i] : NULL);
|
|
if (ret)
|
|
return i ? : ret;
|
|
page_mask = 0;
|
|
goto next_page;
|
|
}
|
|
|
|
if (!vma || check_vma_flags(vma, gup_flags))
|
|
return i ? : -EFAULT;
|
|
if (is_vm_hugetlb_page(vma)) {
|
|
i = follow_hugetlb_page(mm, vma, pages, vmas,
|
|
&start, &nr_pages, i,
|
|
gup_flags);
|
|
continue;
|
|
}
|
|
}
|
|
retry:
|
|
/*
|
|
* If we have a pending SIGKILL, don't keep faulting pages and
|
|
* potentially allocating memory.
|
|
*/
|
|
if (unlikely(fatal_signal_pending(current)))
|
|
return i ? i : -ERESTARTSYS;
|
|
cond_resched();
|
|
page = follow_page_mask(vma, start, foll_flags, &page_mask);
|
|
if (!page) {
|
|
int ret;
|
|
ret = faultin_page(tsk, vma, start, &foll_flags,
|
|
nonblocking);
|
|
switch (ret) {
|
|
case 0:
|
|
goto retry;
|
|
case -EFAULT:
|
|
case -ENOMEM:
|
|
case -EHWPOISON:
|
|
return i ? i : ret;
|
|
case -EBUSY:
|
|
return i;
|
|
case -ENOENT:
|
|
goto next_page;
|
|
}
|
|
BUG();
|
|
}
|
|
if (IS_ERR(page))
|
|
return i ? i : PTR_ERR(page);
|
|
if (pages) {
|
|
pages[i] = page;
|
|
flush_anon_page(vma, page, start);
|
|
flush_dcache_page(page);
|
|
page_mask = 0;
|
|
}
|
|
next_page:
|
|
if (vmas) {
|
|
vmas[i] = vma;
|
|
page_mask = 0;
|
|
}
|
|
page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
|
|
if (page_increm > nr_pages)
|
|
page_increm = nr_pages;
|
|
i += page_increm;
|
|
start += page_increm * PAGE_SIZE;
|
|
nr_pages -= page_increm;
|
|
} while (nr_pages);
|
|
return i;
|
|
}
|
|
EXPORT_SYMBOL(__get_user_pages);
|
|
|
|
/*
|
|
* fixup_user_fault() - manually resolve a user page fault
|
|
* @tsk: the task_struct to use for page fault accounting, or
|
|
* NULL if faults are not to be recorded.
|
|
* @mm: mm_struct of target mm
|
|
* @address: user address
|
|
* @fault_flags:flags to pass down to handle_mm_fault()
|
|
*
|
|
* This is meant to be called in the specific scenario where for locking reasons
|
|
* we try to access user memory in atomic context (within a pagefault_disable()
|
|
* section), this returns -EFAULT, and we want to resolve the user fault before
|
|
* trying again.
|
|
*
|
|
* Typically this is meant to be used by the futex code.
|
|
*
|
|
* The main difference with get_user_pages() is that this function will
|
|
* unconditionally call handle_mm_fault() which will in turn perform all the
|
|
* necessary SW fixup of the dirty and young bits in the PTE, while
|
|
* handle_mm_fault() only guarantees to update these in the struct page.
|
|
*
|
|
* This is important for some architectures where those bits also gate the
|
|
* access permission to the page because they are maintained in software. On
|
|
* such architectures, gup() will not be enough to make a subsequent access
|
|
* succeed.
|
|
*
|
|
* This has the same semantics wrt the @mm->mmap_sem as does filemap_fault().
|
|
*/
|
|
int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
|
|
unsigned long address, unsigned int fault_flags)
|
|
{
|
|
struct vm_area_struct *vma;
|
|
vm_flags_t vm_flags;
|
|
int ret;
|
|
|
|
vma = find_extend_vma(mm, address);
|
|
if (!vma || address < vma->vm_start)
|
|
return -EFAULT;
|
|
|
|
vm_flags = (fault_flags & FAULT_FLAG_WRITE) ? VM_WRITE : VM_READ;
|
|
if (!(vm_flags & vma->vm_flags))
|
|
return -EFAULT;
|
|
|
|
ret = handle_mm_fault(mm, vma, address, fault_flags);
|
|
if (ret & VM_FAULT_ERROR) {
|
|
if (ret & VM_FAULT_OOM)
|
|
return -ENOMEM;
|
|
if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
|
|
return -EHWPOISON;
|
|
if (ret & VM_FAULT_SIGBUS)
|
|
return -EFAULT;
|
|
BUG();
|
|
}
|
|
if (tsk) {
|
|
if (ret & VM_FAULT_MAJOR)
|
|
tsk->maj_flt++;
|
|
else
|
|
tsk->min_flt++;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* get_user_pages() - pin user pages in memory
|
|
* @tsk: the task_struct to use for page fault accounting, or
|
|
* NULL if faults are not to be recorded.
|
|
* @mm: mm_struct of target mm
|
|
* @start: starting user address
|
|
* @nr_pages: number of pages from start to pin
|
|
* @write: whether pages will be written to by the caller
|
|
* @force: whether to force access even when user mapping is currently
|
|
* protected (but never forces write access to shared mapping).
|
|
* @pages: array that receives pointers to the pages pinned.
|
|
* Should be at least nr_pages long. Or NULL, if caller
|
|
* only intends to ensure the pages are faulted in.
|
|
* @vmas: array of pointers to vmas corresponding to each page.
|
|
* Or NULL if the caller does not require them.
|
|
*
|
|
* Returns number of pages pinned. This may be fewer than the number
|
|
* requested. If nr_pages is 0 or negative, returns 0. If no pages
|
|
* were pinned, returns -errno. Each page returned must be released
|
|
* with a put_page() call when it is finished with. vmas will only
|
|
* remain valid while mmap_sem is held.
|
|
*
|
|
* Must be called with mmap_sem held for read or write.
|
|
*
|
|
* get_user_pages walks a process's page tables and takes a reference to
|
|
* each struct page that each user address corresponds to at a given
|
|
* instant. That is, it takes the page that would be accessed if a user
|
|
* thread accesses the given user virtual address at that instant.
|
|
*
|
|
* This does not guarantee that the page exists in the user mappings when
|
|
* get_user_pages returns, and there may even be a completely different
|
|
* page there in some cases (eg. if mmapped pagecache has been invalidated
|
|
* and subsequently re faulted). However it does guarantee that the page
|
|
* won't be freed completely. And mostly callers simply care that the page
|
|
* contains data that was valid *at some point in time*. Typically, an IO
|
|
* or similar operation cannot guarantee anything stronger anyway because
|
|
* locks can't be held over the syscall boundary.
|
|
*
|
|
* If write=0, the page must not be written to. If the page is written to,
|
|
* set_page_dirty (or set_page_dirty_lock, as appropriate) must be called
|
|
* after the page is finished with, and before put_page is called.
|
|
*
|
|
* get_user_pages is typically used for fewer-copy IO operations, to get a
|
|
* handle on the memory by some means other than accesses via the user virtual
|
|
* addresses. The pages may be submitted for DMA to devices or accessed via
|
|
* their kernel linear mapping (via the kmap APIs). Care should be taken to
|
|
* use the correct cache flushing APIs.
|
|
*
|
|
* See also get_user_pages_fast, for performance critical applications.
|
|
*/
|
|
long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
|
|
unsigned long start, unsigned long nr_pages, int write,
|
|
int force, struct page **pages, struct vm_area_struct **vmas)
|
|
{
|
|
int flags = FOLL_TOUCH;
|
|
|
|
if (pages)
|
|
flags |= FOLL_GET;
|
|
if (write)
|
|
flags |= FOLL_WRITE;
|
|
if (force)
|
|
flags |= FOLL_FORCE;
|
|
|
|
return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas,
|
|
NULL);
|
|
}
|
|
EXPORT_SYMBOL(get_user_pages);
|
|
|
|
/**
|
|
* get_dump_page() - pin user page in memory while writing it to core dump
|
|
* @addr: user address
|
|
*
|
|
* Returns struct page pointer of user page pinned for dump,
|
|
* to be freed afterwards by page_cache_release() or put_page().
|
|
*
|
|
* Returns NULL on any kind of failure - a hole must then be inserted into
|
|
* the corefile, to preserve alignment with its headers; and also returns
|
|
* NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
|
|
* allowing a hole to be left in the corefile to save diskspace.
|
|
*
|
|
* Called without mmap_sem, but after all other threads have been killed.
|
|
*/
|
|
#ifdef CONFIG_ELF_CORE
|
|
struct page *get_dump_page(unsigned long addr)
|
|
{
|
|
struct vm_area_struct *vma;
|
|
struct page *page;
|
|
|
|
if (__get_user_pages(current, current->mm, addr, 1,
|
|
FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
|
|
NULL) < 1)
|
|
return NULL;
|
|
flush_cache_page(vma, addr, page_to_pfn(page));
|
|
return page;
|
|
}
|
|
#endif /* CONFIG_ELF_CORE */
|
|
|
|
/*
|
|
* Generic RCU Fast GUP
|
|
*
|
|
* get_user_pages_fast attempts to pin user pages by walking the page
|
|
* tables directly and avoids taking locks. Thus the walker needs to be
|
|
* protected from page table pages being freed from under it, and should
|
|
* block any THP splits.
|
|
*
|
|
* One way to achieve this is to have the walker disable interrupts, and
|
|
* rely on IPIs from the TLB flushing code blocking before the page table
|
|
* pages are freed. This is unsuitable for architectures that do not need
|
|
* to broadcast an IPI when invalidating TLBs.
|
|
*
|
|
* Another way to achieve this is to batch up page table containing pages
|
|
* belonging to more than one mm_user, then rcu_sched a callback to free those
|
|
* pages. Disabling interrupts will allow the fast_gup walker to both block
|
|
* the rcu_sched callback, and an IPI that we broadcast for splitting THPs
|
|
* (which is a relatively rare event). The code below adopts this strategy.
|
|
*
|
|
* Before activating this code, please be aware that the following assumptions
|
|
* are currently made:
|
|
*
|
|
* *) HAVE_RCU_TABLE_FREE is enabled, and tlb_remove_table is used to free
|
|
* pages containing page tables.
|
|
*
|
|
* *) THP splits will broadcast an IPI, this can be achieved by overriding
|
|
* pmdp_splitting_flush.
|
|
*
|
|
* *) ptes can be read atomically by the architecture.
|
|
*
|
|
* *) access_ok is sufficient to validate userspace address ranges.
|
|
*
|
|
* The last two assumptions can be relaxed by the addition of helper functions.
|
|
*
|
|
* This code is based heavily on the PowerPC implementation by Nick Piggin.
|
|
*/
|
|
#ifdef CONFIG_HAVE_GENERIC_RCU_GUP
|
|
|
|
#ifdef __HAVE_ARCH_PTE_SPECIAL
|
|
static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
|
|
int write, struct page **pages, int *nr)
|
|
{
|
|
pte_t *ptep, *ptem;
|
|
int ret = 0;
|
|
|
|
ptem = ptep = pte_offset_map(&pmd, addr);
|
|
do {
|
|
/*
|
|
* In the line below we are assuming that the pte can be read
|
|
* atomically. If this is not the case for your architecture,
|
|
* please wrap this in a helper function!
|
|
*
|
|
* for an example see gup_get_pte in arch/x86/mm/gup.c
|
|
*/
|
|
pte_t pte = ACCESS_ONCE(*ptep);
|
|
struct page *page;
|
|
|
|
/*
|
|
* Similar to the PMD case below, NUMA hinting must take slow
|
|
* path
|
|
*/
|
|
if (!pte_present(pte) || pte_special(pte) ||
|
|
pte_numa(pte) || (write && !pte_write(pte)))
|
|
goto pte_unmap;
|
|
|
|
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
|
|
page = pte_page(pte);
|
|
|
|
if (!page_cache_get_speculative(page))
|
|
goto pte_unmap;
|
|
|
|
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
|
|
put_page(page);
|
|
goto pte_unmap;
|
|
}
|
|
|
|
pages[*nr] = page;
|
|
(*nr)++;
|
|
|
|
} while (ptep++, addr += PAGE_SIZE, addr != end);
|
|
|
|
ret = 1;
|
|
|
|
pte_unmap:
|
|
pte_unmap(ptem);
|
|
return ret;
|
|
}
|
|
#else
|
|
|
|
/*
|
|
* If we can't determine whether or not a pte is special, then fail immediately
|
|
* for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
|
|
* to be special.
|
|
*
|
|
* For a futex to be placed on a THP tail page, get_futex_key requires a
|
|
* __get_user_pages_fast implementation that can pin pages. Thus it's still
|
|
* useful to have gup_huge_pmd even if we can't operate on ptes.
|
|
*/
|
|
static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
|
|
int write, struct page **pages, int *nr)
|
|
{
|
|
return 0;
|
|
}
|
|
#endif /* __HAVE_ARCH_PTE_SPECIAL */
|
|
|
|
static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
|
|
unsigned long end, int write, struct page **pages, int *nr)
|
|
{
|
|
struct page *head, *page, *tail;
|
|
int refs;
|
|
|
|
if (write && !pmd_write(orig))
|
|
return 0;
|
|
|
|
refs = 0;
|
|
head = pmd_page(orig);
|
|
page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
|
|
tail = page;
|
|
do {
|
|
VM_BUG_ON_PAGE(compound_head(page) != head, page);
|
|
pages[*nr] = page;
|
|
(*nr)++;
|
|
page++;
|
|
refs++;
|
|
} while (addr += PAGE_SIZE, addr != end);
|
|
|
|
if (!page_cache_add_speculative(head, refs)) {
|
|
*nr -= refs;
|
|
return 0;
|
|
}
|
|
|
|
if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
|
|
*nr -= refs;
|
|
while (refs--)
|
|
put_page(head);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Any tail pages need their mapcount reference taken before we
|
|
* return. (This allows the THP code to bump their ref count when
|
|
* they are split into base pages).
|
|
*/
|
|
while (refs--) {
|
|
if (PageTail(tail))
|
|
get_huge_page_tail(tail);
|
|
tail++;
|
|
}
|
|
|
|
return 1;
|
|
}
|
|
|
|
static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
|
|
unsigned long end, int write, struct page **pages, int *nr)
|
|
{
|
|
struct page *head, *page, *tail;
|
|
int refs;
|
|
|
|
if (write && !pud_write(orig))
|
|
return 0;
|
|
|
|
refs = 0;
|
|
head = pud_page(orig);
|
|
page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
|
|
tail = page;
|
|
do {
|
|
VM_BUG_ON_PAGE(compound_head(page) != head, page);
|
|
pages[*nr] = page;
|
|
(*nr)++;
|
|
page++;
|
|
refs++;
|
|
} while (addr += PAGE_SIZE, addr != end);
|
|
|
|
if (!page_cache_add_speculative(head, refs)) {
|
|
*nr -= refs;
|
|
return 0;
|
|
}
|
|
|
|
if (unlikely(pud_val(orig) != pud_val(*pudp))) {
|
|
*nr -= refs;
|
|
while (refs--)
|
|
put_page(head);
|
|
return 0;
|
|
}
|
|
|
|
while (refs--) {
|
|
if (PageTail(tail))
|
|
get_huge_page_tail(tail);
|
|
tail++;
|
|
}
|
|
|
|
return 1;
|
|
}
|
|
|
|
static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
|
|
int write, struct page **pages, int *nr)
|
|
{
|
|
unsigned long next;
|
|
pmd_t *pmdp;
|
|
|
|
pmdp = pmd_offset(&pud, addr);
|
|
do {
|
|
pmd_t pmd = ACCESS_ONCE(*pmdp);
|
|
|
|
next = pmd_addr_end(addr, end);
|
|
if (pmd_none(pmd) || pmd_trans_splitting(pmd))
|
|
return 0;
|
|
|
|
if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd))) {
|
|
/*
|
|
* NUMA hinting faults need to be handled in the GUP
|
|
* slowpath for accounting purposes and so that they
|
|
* can be serialised against THP migration.
|
|
*/
|
|
if (pmd_numa(pmd))
|
|
return 0;
|
|
|
|
if (!gup_huge_pmd(pmd, pmdp, addr, next, write,
|
|
pages, nr))
|
|
return 0;
|
|
|
|
} else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
|
|
return 0;
|
|
} while (pmdp++, addr = next, addr != end);
|
|
|
|
return 1;
|
|
}
|
|
|
|
static int gup_pud_range(pgd_t *pgdp, unsigned long addr, unsigned long end,
|
|
int write, struct page **pages, int *nr)
|
|
{
|
|
unsigned long next;
|
|
pud_t *pudp;
|
|
|
|
pudp = pud_offset(pgdp, addr);
|
|
do {
|
|
pud_t pud = ACCESS_ONCE(*pudp);
|
|
|
|
next = pud_addr_end(addr, end);
|
|
if (pud_none(pud))
|
|
return 0;
|
|
if (pud_huge(pud)) {
|
|
if (!gup_huge_pud(pud, pudp, addr, next, write,
|
|
pages, nr))
|
|
return 0;
|
|
} else if (!gup_pmd_range(pud, addr, next, write, pages, nr))
|
|
return 0;
|
|
} while (pudp++, addr = next, addr != end);
|
|
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
|
|
* the regular GUP. It will only return non-negative values.
|
|
*/
|
|
int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
|
|
struct page **pages)
|
|
{
|
|
struct mm_struct *mm = current->mm;
|
|
unsigned long addr, len, end;
|
|
unsigned long next, flags;
|
|
pgd_t *pgdp;
|
|
int nr = 0;
|
|
|
|
start &= PAGE_MASK;
|
|
addr = start;
|
|
len = (unsigned long) nr_pages << PAGE_SHIFT;
|
|
end = start + len;
|
|
|
|
if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
|
|
start, len)))
|
|
return 0;
|
|
|
|
/*
|
|
* Disable interrupts. We use the nested form as we can already have
|
|
* interrupts disabled by get_futex_key.
|
|
*
|
|
* With interrupts disabled, we block page table pages from being
|
|
* freed from under us. See mmu_gather_tlb in asm-generic/tlb.h
|
|
* for more details.
|
|
*
|
|
* We do not adopt an rcu_read_lock(.) here as we also want to
|
|
* block IPIs that come from THPs splitting.
|
|
*/
|
|
|
|
local_irq_save(flags);
|
|
pgdp = pgd_offset(mm, addr);
|
|
do {
|
|
next = pgd_addr_end(addr, end);
|
|
if (pgd_none(*pgdp))
|
|
break;
|
|
else if (!gup_pud_range(pgdp, addr, next, write, pages, &nr))
|
|
break;
|
|
} while (pgdp++, addr = next, addr != end);
|
|
local_irq_restore(flags);
|
|
|
|
return nr;
|
|
}
|
|
|
|
/**
|
|
* get_user_pages_fast() - pin user pages in memory
|
|
* @start: starting user address
|
|
* @nr_pages: number of pages from start to pin
|
|
* @write: whether pages will be written to
|
|
* @pages: array that receives pointers to the pages pinned.
|
|
* Should be at least nr_pages long.
|
|
*
|
|
* Attempt to pin user pages in memory without taking mm->mmap_sem.
|
|
* If not successful, it will fall back to taking the lock and
|
|
* calling get_user_pages().
|
|
*
|
|
* Returns number of pages pinned. This may be fewer than the number
|
|
* requested. If nr_pages is 0 or negative, returns 0. If no pages
|
|
* were pinned, returns -errno.
|
|
*/
|
|
int get_user_pages_fast(unsigned long start, int nr_pages, int write,
|
|
struct page **pages)
|
|
{
|
|
struct mm_struct *mm = current->mm;
|
|
int nr, ret;
|
|
|
|
start &= PAGE_MASK;
|
|
nr = __get_user_pages_fast(start, nr_pages, write, pages);
|
|
ret = nr;
|
|
|
|
if (nr < nr_pages) {
|
|
/* Try to get the remaining pages with get_user_pages */
|
|
start += nr << PAGE_SHIFT;
|
|
pages += nr;
|
|
|
|
down_read(&mm->mmap_sem);
|
|
ret = get_user_pages(current, mm, start,
|
|
nr_pages - nr, write, 0, pages, NULL);
|
|
up_read(&mm->mmap_sem);
|
|
|
|
/* Have to be a bit careful with return values */
|
|
if (nr > 0) {
|
|
if (ret < 0)
|
|
ret = nr;
|
|
else
|
|
ret += nr;
|
|
}
|
|
}
|
|
|
|
return ret;
|
|
}
|
|
|
|
#endif /* CONFIG_HAVE_GENERIC_RCU_GUP */
|