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![Alistair Popple](/assets/img/avatar_default.png)
Some devices require exclusive write access to shared virtual memory (SVM) ranges to perform atomic operations on that memory. This requires CPU page tables to be updated to deny access whilst atomic operations are occurring. In order to do this introduce a new swap entry type (SWP_DEVICE_EXCLUSIVE). When a SVM range needs to be marked for exclusive access by a device all page table mappings for the particular range are replaced with device exclusive swap entries. This causes any CPU access to the page to result in a fault. Faults are resovled by replacing the faulting entry with the original mapping. This results in MMU notifiers being called which a driver uses to update access permissions such as revoking atomic access. After notifiers have been called the device will no longer have exclusive access to the region. Walking of the page tables to find the target pages is handled by get_user_pages() rather than a direct page table walk. A direct page table walk similar to what migrate_vma_collect()/unmap() does could also have been utilised. However this resulted in more code similar in functionality to what get_user_pages() provides as page faulting is required to make the PTEs present and to break COW. [dan.carpenter@oracle.com: fix signedness bug in make_device_exclusive_range()] Link: https://lkml.kernel.org/r/YNIz5NVnZ5GiZ3u1@mwanda Link: https://lkml.kernel.org/r/20210616105937.23201-8-apopple@nvidia.com Signed-off-by: Alistair Popple <apopple@nvidia.com> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Cc: Ben Skeggs <bskeggs@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Peter Xu <peterx@redhat.com> Cc: Ralph Campbell <rcampbell@nvidia.com> Cc: Shakeel Butt <shakeelb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
322 lines
8.7 KiB
C
322 lines
8.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/mm.h>
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#include <linux/rmap.h>
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#include <linux/hugetlb.h>
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#include <linux/swap.h>
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#include <linux/swapops.h>
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#include "internal.h"
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static inline bool not_found(struct page_vma_mapped_walk *pvmw)
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{
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page_vma_mapped_walk_done(pvmw);
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return false;
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}
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static bool map_pte(struct page_vma_mapped_walk *pvmw)
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{
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pvmw->pte = pte_offset_map(pvmw->pmd, pvmw->address);
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if (!(pvmw->flags & PVMW_SYNC)) {
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if (pvmw->flags & PVMW_MIGRATION) {
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if (!is_swap_pte(*pvmw->pte))
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return false;
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} else {
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/*
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* We get here when we are trying to unmap a private
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* device page from the process address space. Such
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* page is not CPU accessible and thus is mapped as
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* a special swap entry, nonetheless it still does
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* count as a valid regular mapping for the page (and
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* is accounted as such in page maps count).
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*
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* So handle this special case as if it was a normal
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* page mapping ie lock CPU page table and returns
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* true.
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*
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* For more details on device private memory see HMM
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* (include/linux/hmm.h or mm/hmm.c).
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*/
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if (is_swap_pte(*pvmw->pte)) {
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swp_entry_t entry;
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/* Handle un-addressable ZONE_DEVICE memory */
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entry = pte_to_swp_entry(*pvmw->pte);
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if (!is_device_private_entry(entry) &&
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!is_device_exclusive_entry(entry))
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return false;
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} else if (!pte_present(*pvmw->pte))
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return false;
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}
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}
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pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
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spin_lock(pvmw->ptl);
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return true;
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}
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static inline bool pfn_is_match(struct page *page, unsigned long pfn)
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{
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unsigned long page_pfn = page_to_pfn(page);
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/* normal page and hugetlbfs page */
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if (!PageTransCompound(page) || PageHuge(page))
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return page_pfn == pfn;
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/* THP can be referenced by any subpage */
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return pfn >= page_pfn && pfn - page_pfn < thp_nr_pages(page);
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}
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/**
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* check_pte - check if @pvmw->page is mapped at the @pvmw->pte
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* @pvmw: page_vma_mapped_walk struct, includes a pair pte and page for checking
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*
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* page_vma_mapped_walk() found a place where @pvmw->page is *potentially*
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* mapped. check_pte() has to validate this.
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*
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* pvmw->pte may point to empty PTE, swap PTE or PTE pointing to
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* arbitrary page.
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*
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* If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
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* entry that points to @pvmw->page or any subpage in case of THP.
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*
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* If PVMW_MIGRATION flag is not set, returns true if pvmw->pte points to
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* pvmw->page or any subpage in case of THP.
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*
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* Otherwise, return false.
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*
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*/
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static bool check_pte(struct page_vma_mapped_walk *pvmw)
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{
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unsigned long pfn;
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if (pvmw->flags & PVMW_MIGRATION) {
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swp_entry_t entry;
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if (!is_swap_pte(*pvmw->pte))
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return false;
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entry = pte_to_swp_entry(*pvmw->pte);
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if (!is_migration_entry(entry) &&
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!is_device_exclusive_entry(entry))
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return false;
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pfn = swp_offset(entry);
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} else if (is_swap_pte(*pvmw->pte)) {
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swp_entry_t entry;
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/* Handle un-addressable ZONE_DEVICE memory */
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entry = pte_to_swp_entry(*pvmw->pte);
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if (!is_device_private_entry(entry) &&
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!is_device_exclusive_entry(entry))
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return false;
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pfn = swp_offset(entry);
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} else {
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if (!pte_present(*pvmw->pte))
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return false;
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pfn = pte_pfn(*pvmw->pte);
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}
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return pfn_is_match(pvmw->page, pfn);
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}
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static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)
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{
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pvmw->address = (pvmw->address + size) & ~(size - 1);
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if (!pvmw->address)
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pvmw->address = ULONG_MAX;
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}
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/**
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* page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at
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* @pvmw->address
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* @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
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* must be set. pmd, pte and ptl must be NULL.
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*
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* Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
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* to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
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* adjusted if needed (for PTE-mapped THPs).
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*
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* If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
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* (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
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* a loop to find all PTEs that map the THP.
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*
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* For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
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* regardless of which page table level the page is mapped at. @pvmw->pmd is
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* NULL.
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*
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* Returns false if there are no more page table entries for the page in
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* the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
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*
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* If you need to stop the walk before page_vma_mapped_walk() returned false,
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* use page_vma_mapped_walk_done(). It will do the housekeeping.
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*/
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bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
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{
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struct mm_struct *mm = pvmw->vma->vm_mm;
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struct page *page = pvmw->page;
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unsigned long end;
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pgd_t *pgd;
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p4d_t *p4d;
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pud_t *pud;
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pmd_t pmde;
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/* The only possible pmd mapping has been handled on last iteration */
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if (pvmw->pmd && !pvmw->pte)
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return not_found(pvmw);
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if (unlikely(PageHuge(page))) {
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/* The only possible mapping was handled on last iteration */
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if (pvmw->pte)
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return not_found(pvmw);
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/* when pud is not present, pte will be NULL */
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pvmw->pte = huge_pte_offset(mm, pvmw->address, page_size(page));
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if (!pvmw->pte)
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return false;
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pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
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spin_lock(pvmw->ptl);
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if (!check_pte(pvmw))
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return not_found(pvmw);
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return true;
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}
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/*
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* Seek to next pte only makes sense for THP.
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* But more important than that optimization, is to filter out
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* any PageKsm page: whose page->index misleads vma_address()
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* and vma_address_end() to disaster.
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*/
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end = PageTransCompound(page) ?
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vma_address_end(page, pvmw->vma) :
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pvmw->address + PAGE_SIZE;
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if (pvmw->pte)
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goto next_pte;
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restart:
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do {
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pgd = pgd_offset(mm, pvmw->address);
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if (!pgd_present(*pgd)) {
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step_forward(pvmw, PGDIR_SIZE);
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continue;
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}
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p4d = p4d_offset(pgd, pvmw->address);
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if (!p4d_present(*p4d)) {
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step_forward(pvmw, P4D_SIZE);
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continue;
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}
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pud = pud_offset(p4d, pvmw->address);
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if (!pud_present(*pud)) {
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step_forward(pvmw, PUD_SIZE);
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continue;
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}
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pvmw->pmd = pmd_offset(pud, pvmw->address);
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/*
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* Make sure the pmd value isn't cached in a register by the
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* compiler and used as a stale value after we've observed a
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* subsequent update.
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*/
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pmde = READ_ONCE(*pvmw->pmd);
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if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
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pvmw->ptl = pmd_lock(mm, pvmw->pmd);
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pmde = *pvmw->pmd;
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if (likely(pmd_trans_huge(pmde))) {
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if (pvmw->flags & PVMW_MIGRATION)
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return not_found(pvmw);
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if (pmd_page(pmde) != page)
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return not_found(pvmw);
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return true;
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}
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if (!pmd_present(pmde)) {
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swp_entry_t entry;
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if (!thp_migration_supported() ||
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!(pvmw->flags & PVMW_MIGRATION))
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return not_found(pvmw);
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entry = pmd_to_swp_entry(pmde);
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if (!is_migration_entry(entry) ||
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pfn_swap_entry_to_page(entry) != page)
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return not_found(pvmw);
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return true;
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}
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/* THP pmd was split under us: handle on pte level */
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spin_unlock(pvmw->ptl);
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pvmw->ptl = NULL;
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} else if (!pmd_present(pmde)) {
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/*
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* If PVMW_SYNC, take and drop THP pmd lock so that we
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* cannot return prematurely, while zap_huge_pmd() has
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* cleared *pmd but not decremented compound_mapcount().
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*/
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if ((pvmw->flags & PVMW_SYNC) &&
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PageTransCompound(page)) {
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spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);
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spin_unlock(ptl);
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}
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step_forward(pvmw, PMD_SIZE);
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continue;
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}
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if (!map_pte(pvmw))
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goto next_pte;
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this_pte:
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if (check_pte(pvmw))
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return true;
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next_pte:
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do {
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pvmw->address += PAGE_SIZE;
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if (pvmw->address >= end)
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return not_found(pvmw);
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/* Did we cross page table boundary? */
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if ((pvmw->address & (PMD_SIZE - PAGE_SIZE)) == 0) {
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if (pvmw->ptl) {
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spin_unlock(pvmw->ptl);
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pvmw->ptl = NULL;
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}
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pte_unmap(pvmw->pte);
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pvmw->pte = NULL;
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goto restart;
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}
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pvmw->pte++;
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if ((pvmw->flags & PVMW_SYNC) && !pvmw->ptl) {
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pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
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spin_lock(pvmw->ptl);
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}
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} while (pte_none(*pvmw->pte));
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if (!pvmw->ptl) {
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pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
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spin_lock(pvmw->ptl);
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}
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goto this_pte;
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} while (pvmw->address < end);
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return false;
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}
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/**
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* page_mapped_in_vma - check whether a page is really mapped in a VMA
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* @page: the page to test
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* @vma: the VMA to test
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*
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* Returns 1 if the page is mapped into the page tables of the VMA, 0
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* if the page is not mapped into the page tables of this VMA. Only
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* valid for normal file or anonymous VMAs.
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*/
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int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
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{
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struct page_vma_mapped_walk pvmw = {
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.page = page,
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.vma = vma,
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.flags = PVMW_SYNC,
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};
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pvmw.address = vma_address(page, vma);
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if (pvmw.address == -EFAULT)
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return 0;
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if (!page_vma_mapped_walk(&pvmw))
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return 0;
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page_vma_mapped_walk_done(&pvmw);
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return 1;
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}
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