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2b4847e730
Base pages are unmapped and flushed from cache and TLB during normal
page migration and replaced with a migration entry that causes any
parallel NUMA hinting fault or gup to block until migration completes.
THP does not unmap pages due to a lack of support for migration entries
at a PMD level. This allows races with get_user_pages and
get_user_pages_fast which commit 3f926ab945
("mm: Close races between
THP migration and PMD numa clearing") made worse by introducing a
pmd_clear_flush().
This patch forces get_user_page (fast and normal) on a pmd_numa page to
go through the slow get_user_page path where it will serialise against
THP migration and properly account for the NUMA hinting fault. On the
migration side the page table lock is taken for each PTE update.
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Alex Thorlton <athorlton@sgi.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
407 lines
10 KiB
C
407 lines
10 KiB
C
/*
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* Lockless get_user_pages_fast for x86
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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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*/
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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 <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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#ifndef CONFIG_X86_PAE
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return ACCESS_ONCE(*ptep);
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#else
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/*
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* With get_user_pages_fast, we walk down the pagetables without taking
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* any locks. For this we would like to load the pointers atomically,
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* but that is not possible (without expensive cmpxchg8b) on PAE. What
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* we do have is the guarantee that a pte will only either go from not
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* present to present, or present to not present or both -- it will not
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* switch to a completely different present page without a TLB flush in
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* between; something that we are blocking by holding interrupts off.
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*
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* Setting ptes from not present to present goes:
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* ptep->pte_high = h;
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* smp_wmb();
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* ptep->pte_low = l;
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*
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* And present to not present goes:
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* ptep->pte_low = 0;
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* smp_wmb();
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* ptep->pte_high = 0;
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*
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* We must ensure here that the load of pte_low sees l iff pte_high
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* sees h. We load pte_high *after* loading pte_low, which ensures we
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* don't see an older value of pte_high. *Then* we recheck pte_low,
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* which ensures that we haven't picked up a changed pte high. We might
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* have got rubbish values from pte_low and pte_high, but we are
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* guaranteed that pte_low will not have the present bit set *unless*
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* it is 'l'. And get_user_pages_fast only operates on present ptes, so
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* we're safe.
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*
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* gup_get_pte should not be used or copied outside gup.c without being
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* very careful -- it does not atomically load the pte or anything that
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* is likely to be useful for you.
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*/
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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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#endif
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}
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/*
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* The performance critical leaf functions are made noinline otherwise gcc
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* inlines everything into a single function which results in too much
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* register pressure.
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*/
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static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
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unsigned long end, int write, struct page **pages, int *nr)
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{
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unsigned long mask;
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pte_t *ptep;
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mask = _PAGE_PRESENT|_PAGE_USER;
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if (write)
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mask |= _PAGE_RW;
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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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/* Similar to the PMD case, NUMA hinting must take slow path */
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if (pte_numa(pte)) {
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pte_unmap(ptep);
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return 0;
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}
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if ((pte_flags(pte) & (mask | _PAGE_SPECIAL)) != mask) {
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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 noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
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unsigned long end, int write, struct page **pages, int *nr)
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{
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unsigned long mask;
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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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mask = _PAGE_PRESENT|_PAGE_USER;
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if (write)
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mask |= _PAGE_RW;
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if ((pte_flags(pte) & mask) != mask)
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return 0;
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/* hugepages are never "special" */
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VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
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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_large(pmd))) {
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/*
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* NUMA hinting faults need to be handled in the GUP
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* slowpath for accounting purposes and so that they
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* can be serialised against THP migration.
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*/
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if (pmd_numa(pmd))
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return 0;
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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 noinline int gup_huge_pud(pud_t pud, unsigned long addr,
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unsigned long end, int write, struct page **pages, int *nr)
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{
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unsigned long mask;
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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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mask = _PAGE_PRESENT|_PAGE_USER;
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if (write)
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mask |= _PAGE_RW;
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if ((pte_flags(pte) & mask) != mask)
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return 0;
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/* hugepages are never "special" */
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VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
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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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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_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_large(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 size
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* 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 on x86.
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*
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* So long as we atomically load page table pointers versus teardown
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* (which we do on x86, with the above PAE exception), we can follow the
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* address down to the 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 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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#ifdef CONFIG_X86_64
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if (end >> __VIRTUAL_MASK_SHIFT)
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goto slow_irqon;
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#endif
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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 size
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* 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 on x86.
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*
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* So long as we atomically load page table pointers versus teardown
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* (which we do on x86, with the above PAE exception), we can follow the
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* address down to the the page and take a ref on it.
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*/
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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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{
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int ret;
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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, 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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}
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