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@@ -0,0 +1,496 @@
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+/*
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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 <linux/memremap.h>
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+
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+#include <asm/mmu_context.h>
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+#include <asm/pgtable.h>
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+
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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 READ_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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+
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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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+
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+ return pte;
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+#endif
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+}
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+
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+static void undo_dev_pagemap(int *nr, int nr_start, struct page **pages)
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+{
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+ while ((*nr) - nr_start) {
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+ struct page *page = pages[--(*nr)];
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+
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+ ClearPageReferenced(page);
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+ put_page(page);
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+ }
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+}
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+
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+/*
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+ * 'pteval' can come from a pte, pmd, pud or p4d. We only check
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+ * _PAGE_PRESENT, _PAGE_USER, and _PAGE_RW in here which are the
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+ * same value on all 4 types.
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+ */
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+static inline int pte_allows_gup(unsigned long pteval, int write)
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+{
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+ unsigned long need_pte_bits = _PAGE_PRESENT|_PAGE_USER;
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+
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+ if (write)
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+ need_pte_bits |= _PAGE_RW;
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+
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+ if ((pteval & need_pte_bits) != need_pte_bits)
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+ return 0;
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+
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+ /* Check memory protection keys permissions. */
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+ if (!__pkru_allows_pkey(pte_flags_pkey(pteval), write))
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+ return 0;
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+
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+ return 1;
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+}
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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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+ struct dev_pagemap *pgmap = NULL;
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+ int nr_start = *nr, ret = 0;
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+ pte_t *ptep, *ptem;
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+
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+ /*
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+ * Keep the original mapped PTE value (ptem) around since we
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+ * might increment ptep off the end of the page when finishing
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+ * our loop iteration.
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+ */
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+ ptem = 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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+
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+ /* Similar to the PMD case, NUMA hinting must take slow path */
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+ if (pte_protnone(pte))
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+ break;
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+
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+ if (!pte_allows_gup(pte_val(pte), write))
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+ break;
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+
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+ if (pte_devmap(pte)) {
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+ pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
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+ if (unlikely(!pgmap)) {
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+ undo_dev_pagemap(nr, nr_start, pages);
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+ break;
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+ }
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+ } else if (pte_special(pte))
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+ break;
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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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+ put_dev_pagemap(pgmap);
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+ SetPageReferenced(page);
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+ pages[*nr] = page;
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+ (*nr)++;
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+
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+ } while (ptep++, addr += PAGE_SIZE, addr != end);
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+ if (addr == end)
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+ ret = 1;
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+ pte_unmap(ptem);
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+
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+ return ret;
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+}
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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(page != compound_head(page), page);
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+ VM_BUG_ON_PAGE(page_count(page) == 0, page);
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+ page_ref_add(page, nr);
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+ SetPageReferenced(page);
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+}
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+
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+static int __gup_device_huge(unsigned long pfn, unsigned long addr,
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+ unsigned long end, struct page **pages, int *nr)
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+{
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+ int nr_start = *nr;
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+ struct dev_pagemap *pgmap = NULL;
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+
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+ do {
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+ struct page *page = pfn_to_page(pfn);
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+
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+ pgmap = get_dev_pagemap(pfn, pgmap);
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+ if (unlikely(!pgmap)) {
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+ undo_dev_pagemap(nr, nr_start, pages);
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+ return 0;
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+ }
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+ SetPageReferenced(page);
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+ pages[*nr] = page;
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+ get_page(page);
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+ put_dev_pagemap(pgmap);
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+ (*nr)++;
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+ pfn++;
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+ } while (addr += PAGE_SIZE, addr != end);
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+ return 1;
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+}
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+
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+static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
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+ unsigned long end, struct page **pages, int *nr)
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+{
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+ unsigned long fault_pfn;
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+
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+ fault_pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
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+ return __gup_device_huge(fault_pfn, addr, end, pages, nr);
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+}
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+
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+static int __gup_device_huge_pud(pud_t pud, unsigned long addr,
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+ unsigned long end, struct page **pages, int *nr)
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+{
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+ unsigned long fault_pfn;
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+
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+ fault_pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
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+ return __gup_device_huge(fault_pfn, addr, end, pages, nr);
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+}
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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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+ struct page *head, *page;
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+ int refs;
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+
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+ if (!pte_allows_gup(pmd_val(pmd), write))
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+ return 0;
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+
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+ VM_BUG_ON(!pfn_valid(pmd_pfn(pmd)));
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+ if (pmd_devmap(pmd))
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+ return __gup_device_huge_pmd(pmd, addr, end, pages, nr);
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+
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+ /* hugepages are never "special" */
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+ VM_BUG_ON(pmd_flags(pmd) & _PAGE_SPECIAL);
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+
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+ refs = 0;
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+ head = pmd_page(pmd);
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+ page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
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+ do {
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+ VM_BUG_ON_PAGE(compound_head(page) != head, page);
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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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+
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+ return 1;
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+}
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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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+
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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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+
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+ next = pmd_addr_end(addr, end);
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+ if (pmd_none(pmd))
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+ return 0;
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+ if (unlikely(pmd_large(pmd) || !pmd_present(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_protnone(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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+
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+ return 1;
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+}
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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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+ struct page *head, *page;
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+ int refs;
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+
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+ if (!pte_allows_gup(pud_val(pud), write))
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+ return 0;
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+
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+ VM_BUG_ON(!pfn_valid(pud_pfn(pud)));
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+ if (pud_devmap(pud))
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+ return __gup_device_huge_pud(pud, addr, end, pages, nr);
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+
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+ /* hugepages are never "special" */
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+ VM_BUG_ON(pud_flags(pud) & _PAGE_SPECIAL);
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+
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+ refs = 0;
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+ head = pud_page(pud);
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+ page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
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+ do {
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+ VM_BUG_ON_PAGE(compound_head(page) != head, page);
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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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+
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+ return 1;
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+}
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+
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+static int gup_pud_range(p4d_t p4d, 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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+
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+ pudp = pud_offset(&p4d, addr);
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+ do {
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+ pud_t pud = *pudp;
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+
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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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+
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+ return 1;
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+}
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+
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+static int gup_p4d_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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+ p4d_t *p4dp;
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+
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+ p4dp = p4d_offset(&pgd, addr);
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+ do {
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+ p4d_t p4d = *p4dp;
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+
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+ next = p4d_addr_end(addr, end);
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+ if (p4d_none(p4d))
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+ return 0;
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+ BUILD_BUG_ON(p4d_large(p4d));
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+ if (!gup_pud_range(p4d, addr, next, write, pages, nr))
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+ return 0;
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+ } while (p4dp++, addr = next, addr != end);
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+
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+ return 1;
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+}
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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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+
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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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+ /*
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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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+
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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_p4d_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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+
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+ return nr;
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+}
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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
|
|
|
+ * @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;
|
|
|
+ unsigned long addr, len, end;
|
|
|
+ unsigned long next;
|
|
|
+ pgd_t *pgdp;
|
|
|
+ int nr = 0;
|
|
|
+
|
|
|
+ start &= PAGE_MASK;
|
|
|
+ addr = start;
|
|
|
+ len = (unsigned long) nr_pages << PAGE_SHIFT;
|
|
|
+
|
|
|
+ end = start + len;
|
|
|
+ if (end < start)
|
|
|
+ goto slow_irqon;
|
|
|
+
|
|
|
+#ifdef CONFIG_X86_64
|
|
|
+ if (end >> __VIRTUAL_MASK_SHIFT)
|
|
|
+ goto slow_irqon;
|
|
|
+#endif
|
|
|
+
|
|
|
+ /*
|
|
|
+ * XXX: batch / limit 'nr', to avoid large irq off latency
|
|
|
+ * needs some instrumenting to determine the common sizes used by
|
|
|
+ * important workloads (eg. DB2), and whether limiting the batch size
|
|
|
+ * will decrease performance.
|
|
|
+ *
|
|
|
+ * It seems like we're in the clear for the moment. Direct-IO is
|
|
|
+ * the main guy that batches up lots of get_user_pages, and even
|
|
|
+ * they are limited to 64-at-a-time which is not so many.
|
|
|
+ */
|
|
|
+ /*
|
|
|
+ * This doesn't prevent pagetable teardown, but does prevent
|
|
|
+ * the pagetables and pages from being freed on x86.
|
|
|
+ *
|
|
|
+ * So long as we atomically load page table pointers versus teardown
|
|
|
+ * (which we do on x86, with the above PAE exception), we can follow the
|
|
|
+ * address down to the the page and take a ref on it.
|
|
|
+ */
|
|
|
+ local_irq_disable();
|
|
|
+ pgdp = pgd_offset(mm, addr);
|
|
|
+ do {
|
|
|
+ pgd_t pgd = *pgdp;
|
|
|
+
|
|
|
+ next = pgd_addr_end(addr, end);
|
|
|
+ if (pgd_none(pgd))
|
|
|
+ goto slow;
|
|
|
+ if (!gup_p4d_range(pgd, addr, next, write, pages, &nr))
|
|
|
+ goto slow;
|
|
|
+ } while (pgdp++, addr = next, addr != end);
|
|
|
+ local_irq_enable();
|
|
|
+
|
|
|
+ VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
|
|
|
+ return nr;
|
|
|
+
|
|
|
+ {
|
|
|
+ int ret;
|
|
|
+
|
|
|
+slow:
|
|
|
+ local_irq_enable();
|
|
|
+slow_irqon:
|
|
|
+ /* Try to get the remaining pages with get_user_pages */
|
|
|
+ start += nr << PAGE_SHIFT;
|
|
|
+ pages += nr;
|
|
|
+
|
|
|
+ ret = get_user_pages_unlocked(start,
|
|
|
+ (end - start) >> PAGE_SHIFT,
|
|
|
+ pages, write ? FOLL_WRITE : 0);
|
|
|
+
|
|
|
+ /* Have to be a bit careful with return values */
|
|
|
+ if (nr > 0) {
|
|
|
+ if (ret < 0)
|
|
|
+ ret = nr;
|
|
|
+ else
|
|
|
+ ret += nr;
|
|
|
+ }
|
|
|
+
|
|
|
+ return ret;
|
|
|
+ }
|
|
|
+}
|
Ingo Molnar