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MIPS: Add fast get_user_pages
Gup is used in a few cases, say futex. This work is derived from the x86 version, and operations of pte and pmd are adapted to the defines of MIPS in straight forward manner. [ralf@linux-mips.org: Fixed up reject in arch/mips/mm/Makefile due to whitespace formatting differences. Fixed build error in gup.c due to conflicting changes elsewhere in the kernel.] Signed-off-by: Hillf Danton <dhillf@gmail.com> Cc: David Daney <david.daney@cavium.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/2859/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
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parent
5639bc4a64
commit
b1c10bea62
2 changed files with 317 additions and 2 deletions
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@ -3,8 +3,8 @@
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#
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obj-y += cache.o dma-default.o extable.o fault.o \
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init.o mmap.o tlbex.o tlbex-fault.o uasm.o \
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page.o
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gup.o init.o mmap.o page.o tlbex.o \
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tlbex-fault.o uasm.o
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obj-$(CONFIG_32BIT) += ioremap.o pgtable-32.o
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obj-$(CONFIG_64BIT) += pgtable-64.o
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315
arch/mips/mm/gup.c
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315
arch/mips/mm/gup.c
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@ -0,0 +1,315 @@
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/*
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* Lockless get_user_pages_fast for MIPS
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*
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* Copyright (C) 2008 Nick Piggin
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* Copyright (C) 2008 Novell Inc.
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* Copyright (C) 2011 Ralf Baechle
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*/
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#include <linux/sched.h>
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#include <linux/mm.h>
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#include <linux/vmstat.h>
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#include <linux/highmem.h>
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#include <linux/swap.h>
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#include <linux/hugetlb.h>
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#include <asm/pgtable.h>
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static inline pte_t gup_get_pte(pte_t *ptep)
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{
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#if defined(CONFIG_64BIT_PHYS_ADDR) && defined(CONFIG_CPU_MIPS32)
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pte_t pte;
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retry:
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pte.pte_low = ptep->pte_low;
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smp_rmb();
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pte.pte_high = ptep->pte_high;
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smp_rmb();
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if (unlikely(pte.pte_low != ptep->pte_low))
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goto retry;
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return pte;
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#else
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return ACCESS_ONCE(*ptep);
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#endif
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}
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static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
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int write, struct page **pages, int *nr)
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{
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pte_t *ptep = pte_offset_map(&pmd, addr);
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do {
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pte_t pte = gup_get_pte(ptep);
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struct page *page;
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if (!pte_present(pte) ||
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pte_special(pte) || (write && !pte_write(pte))) {
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pte_unmap(ptep);
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return 0;
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}
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VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
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page = pte_page(pte);
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get_page(page);
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SetPageReferenced(page);
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pages[*nr] = page;
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(*nr)++;
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} while (ptep++, addr += PAGE_SIZE, addr != end);
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pte_unmap(ptep - 1);
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return 1;
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}
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static inline void get_head_page_multiple(struct page *page, int nr)
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{
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VM_BUG_ON(page != compound_head(page));
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VM_BUG_ON(page_count(page) == 0);
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atomic_add(nr, &page->_count);
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SetPageReferenced(page);
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}
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static int gup_huge_pmd(pmd_t pmd, unsigned long addr, unsigned long end,
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int write, struct page **pages, int *nr)
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{
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pte_t pte = *(pte_t *)&pmd;
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struct page *head, *page;
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int refs;
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if (write && !pte_write(pte))
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return 0;
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/* hugepages are never "special" */
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VM_BUG_ON(pte_special(pte));
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VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
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refs = 0;
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head = pte_page(pte);
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page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
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do {
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VM_BUG_ON(compound_head(page) != head);
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pages[*nr] = page;
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if (PageTail(page))
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get_huge_page_tail(page);
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(*nr)++;
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page++;
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refs++;
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} while (addr += PAGE_SIZE, addr != end);
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get_head_page_multiple(head, refs);
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return 1;
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}
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static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
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int write, struct page **pages, int *nr)
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{
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unsigned long next;
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pmd_t *pmdp;
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pmdp = pmd_offset(&pud, addr);
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do {
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pmd_t pmd = *pmdp;
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next = pmd_addr_end(addr, end);
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/*
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* The pmd_trans_splitting() check below explains why
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* pmdp_splitting_flush has to flush the tlb, to stop
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* this gup-fast code from running while we set the
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* splitting bit in the pmd. Returning zero will take
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* the slow path that will call wait_split_huge_page()
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* if the pmd is still in splitting state. gup-fast
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* can't because it has irq disabled and
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* wait_split_huge_page() would never return as the
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* tlb flush IPI wouldn't run.
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*/
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if (pmd_none(pmd) || pmd_trans_splitting(pmd))
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return 0;
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if (unlikely(pmd_huge(pmd))) {
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if (!gup_huge_pmd(pmd, addr, next, write, pages,nr))
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return 0;
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} else {
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if (!gup_pte_range(pmd, addr, next, write, pages,nr))
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return 0;
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}
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} while (pmdp++, addr = next, addr != end);
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return 1;
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}
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static int gup_huge_pud(pud_t pud, unsigned long addr, unsigned long end,
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int write, struct page **pages, int *nr)
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{
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pte_t pte = *(pte_t *)&pud;
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struct page *head, *page;
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int refs;
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if (write && !pte_write(pte))
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return 0;
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/* hugepages are never "special" */
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VM_BUG_ON(pte_special(pte));
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VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
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refs = 0;
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head = pte_page(pte);
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page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
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do {
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VM_BUG_ON(compound_head(page) != head);
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pages[*nr] = page;
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(*nr)++;
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page++;
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refs++;
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} while (addr += PAGE_SIZE, addr != end);
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get_head_page_multiple(head, refs);
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return 1;
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}
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static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
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int write, struct page **pages, int *nr)
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{
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unsigned long next;
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pud_t *pudp;
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pudp = pud_offset(&pgd, addr);
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do {
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pud_t pud = *pudp;
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next = pud_addr_end(addr, end);
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if (pud_none(pud))
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return 0;
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if (unlikely(pud_huge(pud))) {
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if (!gup_huge_pud(pud, addr, next, write, pages,nr))
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return 0;
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} else {
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if (!gup_pmd_range(pud, addr, next, write, pages,nr))
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return 0;
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}
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} while (pudp++, addr = next, addr != end);
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return 1;
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}
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/*
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* Like get_user_pages_fast() except its IRQ-safe in that it won't fall
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* back to the regular GUP.
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*/
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int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
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struct page **pages)
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{
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struct mm_struct *mm = current->mm;
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unsigned long addr, len, end;
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unsigned long next;
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unsigned long flags;
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pgd_t *pgdp;
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int nr = 0;
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start &= PAGE_MASK;
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addr = start;
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len = (unsigned long) nr_pages << PAGE_SHIFT;
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end = start + len;
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if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
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(void __user *)start, len)))
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return 0;
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/*
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* XXX: batch / limit 'nr', to avoid large irq off latency
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* needs some instrumenting to determine the common sizes used by
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* important workloads (eg. DB2), and whether limiting the batch
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* size will decrease performance.
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*
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* It seems like we're in the clear for the moment. Direct-IO is
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* the main guy that batches up lots of get_user_pages, and even
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* they are limited to 64-at-a-time which is not so many.
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*/
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/*
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* This doesn't prevent pagetable teardown, but does prevent
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* the pagetables and pages from being freed.
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*
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* So long as we atomically load page table pointers versus teardown,
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* we can follow the address down to the page and take a ref on it.
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*/
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local_irq_save(flags);
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pgdp = pgd_offset(mm, addr);
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do {
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pgd_t pgd = *pgdp;
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next = pgd_addr_end(addr, end);
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if (pgd_none(pgd))
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break;
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if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
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break;
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} while (pgdp++, addr = next, addr != end);
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local_irq_restore(flags);
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return nr;
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}
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/**
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* get_user_pages_fast() - pin user pages in memory
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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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* @write: whether pages will be written to
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* @pages: array that receives pointers to the pages pinned.
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* Should be at least nr_pages long.
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*
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* Attempt to pin user pages in memory without taking mm->mmap_sem.
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* If not successful, it will fall back to taking the lock and
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* calling get_user_pages().
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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.
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*/
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int get_user_pages_fast(unsigned long start, int nr_pages, int write,
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struct page **pages)
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{
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struct mm_struct *mm = current->mm;
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unsigned long addr, len, end;
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unsigned long next;
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pgd_t *pgdp;
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int ret, nr = 0;
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start &= PAGE_MASK;
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addr = start;
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len = (unsigned long) nr_pages << PAGE_SHIFT;
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end = start + len;
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if (end < start)
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goto slow_irqon;
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/* XXX: batch / limit 'nr' */
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local_irq_disable();
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pgdp = pgd_offset(mm, addr);
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do {
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pgd_t pgd = *pgdp;
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next = pgd_addr_end(addr, end);
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if (pgd_none(pgd))
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goto slow;
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if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
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goto slow;
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} while (pgdp++, addr = next, addr != end);
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local_irq_enable();
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VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
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return nr;
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slow:
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local_irq_enable();
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slow_irqon:
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/* Try to get the remaining pages with get_user_pages */
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start += nr << PAGE_SHIFT;
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pages += nr;
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down_read(&mm->mmap_sem);
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ret = get_user_pages(current, mm, start,
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(end - start) >> PAGE_SHIFT,
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write, 0, pages, NULL);
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up_read(&mm->mmap_sem);
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/* Have to be a bit careful with return values */
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if (nr > 0) {
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if (ret < 0)
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ret = nr;
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else
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ret += nr;
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}
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return ret;
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}
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