Merge branch 'perfcounters-fixes-for-linus' of git://git.kernel.org/pub/scm/linux...

[mv-sheeva.git] / arch / x86 / mm / gup.c

diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index f974809412692190b2dd3fb7f7b0ca85bdcf838f..71da1bca13cbb9fde26f59100f1b9b3b30f3a8e5 100644 (file)
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -14,7 +14,7 @@
 static inline pte_t gup_get_pte(pte_t *ptep)
 {
 #ifndef CONFIG_X86_PAE
-       return *ptep;
+       return ACCESS_ONCE(*ptep);
 #else
        /*
         * With get_user_pages_fast, we walk down the pagetables without taking
@@ -219,6 +219,62 @@ static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
        return 1;
 }
 
+/*
+ * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
+ * back to the regular GUP.
+ */
+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;
+       unsigned long flags;
+       pgd_t *pgdp;
+       int nr = 0;
+
+       start &= PAGE_MASK;
+       addr = start;
+       len = (unsigned long) nr_pages << PAGE_SHIFT;
+       end = start + len;
+       if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
+                                       (void __user *)start, len)))
+               return 0;
+
+       /*
+        * 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_save(flags);
+       pgdp = pgd_offset(mm, addr);
+       do {
+               pgd_t pgd = *pgdp;
+
+               next = pgd_addr_end(addr, end);
+               if (pgd_none(pgd))
+                       break;
+               if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
+                       break;
+       } while (pgdp++, addr = next, addr != end);
+       local_irq_restore(flags);
+
+       return nr;
+}
+
 /**
  * get_user_pages_fast() - pin user pages in memory
  * @start:     starting user address