|
|
@@ -0,0 +1,258 @@
|
|
|
+/*
|
|
|
+ * Lockless get_user_pages_fast for x86
|
|
|
+ *
|
|
|
+ * Copyright (C) 2008 Nick Piggin
|
|
|
+ * Copyright (C) 2008 Novell Inc.
|
|
|
+ */
|
|
|
+#include <linux/sched.h>
|
|
|
+#include <linux/mm.h>
|
|
|
+#include <linux/vmstat.h>
|
|
|
+#include <linux/highmem.h>
|
|
|
+
|
|
|
+#include <asm/pgtable.h>
|
|
|
+
|
|
|
+static inline pte_t gup_get_pte(pte_t *ptep)
|
|
|
+{
|
|
|
+#ifndef CONFIG_X86_PAE
|
|
|
+ return *ptep;
|
|
|
+#else
|
|
|
+ /*
|
|
|
+ * With get_user_pages_fast, we walk down the pagetables without taking
|
|
|
+ * any locks. For this we would like to load the pointers atoimcally,
|
|
|
+ * but that is not possible (without expensive cmpxchg8b) on PAE. What
|
|
|
+ * we do have is the guarantee that a pte will only either go from not
|
|
|
+ * present to present, or present to not present or both -- it will not
|
|
|
+ * switch to a completely different present page without a TLB flush in
|
|
|
+ * between; something that we are blocking by holding interrupts off.
|
|
|
+ *
|
|
|
+ * Setting ptes from not present to present goes:
|
|
|
+ * ptep->pte_high = h;
|
|
|
+ * smp_wmb();
|
|
|
+ * ptep->pte_low = l;
|
|
|
+ *
|
|
|
+ * And present to not present goes:
|
|
|
+ * ptep->pte_low = 0;
|
|
|
+ * smp_wmb();
|
|
|
+ * ptep->pte_high = 0;
|
|
|
+ *
|
|
|
+ * We must ensure here that the load of pte_low sees l iff pte_high
|
|
|
+ * sees h. We load pte_high *after* loading pte_low, which ensures we
|
|
|
+ * don't see an older value of pte_high. *Then* we recheck pte_low,
|
|
|
+ * which ensures that we haven't picked up a changed pte high. We might
|
|
|
+ * have got rubbish values from pte_low and pte_high, but we are
|
|
|
+ * guaranteed that pte_low will not have the present bit set *unless*
|
|
|
+ * it is 'l'. And get_user_pages_fast only operates on present ptes, so
|
|
|
+ * we're safe.
|
|
|
+ *
|
|
|
+ * gup_get_pte should not be used or copied outside gup.c without being
|
|
|
+ * very careful -- it does not atomically load the pte or anything that
|
|
|
+ * is likely to be useful for you.
|
|
|
+ */
|
|
|
+ pte_t pte;
|
|
|
+
|
|
|
+retry:
|
|
|
+ pte.pte_low = ptep->pte_low;
|
|
|
+ smp_rmb();
|
|
|
+ pte.pte_high = ptep->pte_high;
|
|
|
+ smp_rmb();
|
|
|
+ if (unlikely(pte.pte_low != ptep->pte_low))
|
|
|
+ goto retry;
|
|
|
+
|
|
|
+ return pte;
|
|
|
+#endif
|
|
|
+}
|
|
|
+
|
|
|
+/*
|
|
|
+ * The performance critical leaf functions are made noinline otherwise gcc
|
|
|
+ * inlines everything into a single function which results in too much
|
|
|
+ * register pressure.
|
|
|
+ */
|
|
|
+static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
|
|
|
+ unsigned long end, int write, struct page **pages, int *nr)
|
|
|
+{
|
|
|
+ unsigned long mask;
|
|
|
+ pte_t *ptep;
|
|
|
+
|
|
|
+ mask = _PAGE_PRESENT|_PAGE_USER;
|
|
|
+ if (write)
|
|
|
+ mask |= _PAGE_RW;
|
|
|
+
|
|
|
+ ptep = pte_offset_map(&pmd, addr);
|
|
|
+ do {
|
|
|
+ pte_t pte = gup_get_pte(ptep);
|
|
|
+ struct page *page;
|
|
|
+
|
|
|
+ if ((pte_val(pte) & (mask | _PAGE_SPECIAL)) != mask) {
|
|
|
+ pte_unmap(ptep);
|
|
|
+ return 0;
|
|
|
+ }
|
|
|
+ VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
|
|
|
+ page = pte_page(pte);
|
|
|
+ get_page(page);
|
|
|
+ pages[*nr] = page;
|
|
|
+ (*nr)++;
|
|
|
+
|
|
|
+ } while (ptep++, addr += PAGE_SIZE, addr != end);
|
|
|
+ pte_unmap(ptep - 1);
|
|
|
+
|
|
|
+ return 1;
|
|
|
+}
|
|
|
+
|
|
|
+static inline void get_head_page_multiple(struct page *page, int nr)
|
|
|
+{
|
|
|
+ VM_BUG_ON(page != compound_head(page));
|
|
|
+ VM_BUG_ON(page_count(page) == 0);
|
|
|
+ atomic_add(nr, &page->_count);
|
|
|
+}
|
|
|
+
|
|
|
+static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
|
|
|
+ unsigned long end, int write, struct page **pages, int *nr)
|
|
|
+{
|
|
|
+ unsigned long mask;
|
|
|
+ pte_t pte = *(pte_t *)&pmd;
|
|
|
+ struct page *head, *page;
|
|
|
+ int refs;
|
|
|
+
|
|
|
+ mask = _PAGE_PRESENT|_PAGE_USER;
|
|
|
+ if (write)
|
|
|
+ mask |= _PAGE_RW;
|
|
|
+ if ((pte_val(pte) & mask) != mask)
|
|
|
+ return 0;
|
|
|
+ /* hugepages are never "special" */
|
|
|
+ VM_BUG_ON(pte_val(pte) & _PAGE_SPECIAL);
|
|
|
+ VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
|
|
|
+
|
|
|
+ refs = 0;
|
|
|
+ head = pte_page(pte);
|
|
|
+ page = head + ((addr & ~HPAGE_MASK) >> PAGE_SHIFT);
|
|
|
+ do {
|
|
|
+ VM_BUG_ON(compound_head(page) != head);
|
|
|
+ pages[*nr] = page;
|
|
|
+ (*nr)++;
|
|
|
+ page++;
|
|
|
+ refs++;
|
|
|
+ } while (addr += PAGE_SIZE, addr != end);
|
|
|
+ get_head_page_multiple(head, refs);
|
|
|
+
|
|
|
+ return 1;
|
|
|
+}
|
|
|
+
|
|
|
+static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
|
|
|
+ int write, struct page **pages, int *nr)
|
|
|
+{
|
|
|
+ unsigned long next;
|
|
|
+ pmd_t *pmdp;
|
|
|
+
|
|
|
+ pmdp = pmd_offset(&pud, addr);
|
|
|
+ do {
|
|
|
+ pmd_t pmd = *pmdp;
|
|
|
+
|
|
|
+ next = pmd_addr_end(addr, end);
|
|
|
+ if (pmd_none(pmd))
|
|
|
+ return 0;
|
|
|
+ if (unlikely(pmd_large(pmd))) {
|
|
|
+ if (!gup_huge_pmd(pmd, addr, next, write, pages, nr))
|
|
|
+ return 0;
|
|
|
+ } else {
|
|
|
+ if (!gup_pte_range(pmd, addr, next, write, pages, nr))
|
|
|
+ return 0;
|
|
|
+ }
|
|
|
+ } while (pmdp++, addr = next, addr != end);
|
|
|
+
|
|
|
+ return 1;
|
|
|
+}
|
|
|
+
|
|
|
+static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
|
|
|
+ int write, struct page **pages, int *nr)
|
|
|
+{
|
|
|
+ unsigned long next;
|
|
|
+ pud_t *pudp;
|
|
|
+
|
|
|
+ pudp = pud_offset(&pgd, addr);
|
|
|
+ do {
|
|
|
+ pud_t pud = *pudp;
|
|
|
+
|
|
|
+ next = pud_addr_end(addr, end);
|
|
|
+ if (pud_none(pud))
|
|
|
+ return 0;
|
|
|
+ if (!gup_pmd_range(pud, addr, next, write, pages, nr))
|
|
|
+ return 0;
|
|
|
+ } while (pudp++, addr = next, addr != end);
|
|
|
+
|
|
|
+ return 1;
|
|
|
+}
|
|
|
+
|
|
|
+int get_user_pages_fast(unsigned long start, int nr_pages, int write,
|
|
|
+ struct page **pages)
|
|
|
+{
|
|
|
+ struct mm_struct *mm = current->mm;
|
|
|
+ unsigned long end = start + (nr_pages << PAGE_SHIFT);
|
|
|
+ unsigned long addr = start;
|
|
|
+ unsigned long next;
|
|
|
+ pgd_t *pgdp;
|
|
|
+ int nr = 0;
|
|
|
+
|
|
|
+ if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
|
|
|
+ start, nr_pages*PAGE_SIZE)))
|
|
|
+ goto slow_irqon;
|
|
|
+
|
|
|
+ /*
|
|
|
+ * 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_pud_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;
|
|
|
+
|
|
|
+ down_read(&mm->mmap_sem);
|
|
|
+ ret = get_user_pages(current, mm, start,
|
|
|
+ (end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
|
|
|
+ up_read(&mm->mmap_sem);
|
|
|
+
|
|
|
+ /* Have to be a bit careful with return values */
|
|
|
+ if (nr > 0) {
|
|
|
+ if (ret < 0)
|
|
|
+ ret = nr;
|
|
|
+ else
|
|
|
+ ret += nr;
|
|
|
+ }
|
|
|
+
|
|
|
+ return ret;
|
|
|
+ }
|
|
|
+}
|
Nick Piggin