On Fri, 2008-03-28 at 04:00 +0100, Nick Piggin wrote:
> +++ linux-2.6/arch/x86/mm/gup.c
> @@ -0,0 +1,198 @@
> +/*
> + * Lockless fast_gup for x86
> + *
> + * Copyright (C) 2007 Nick Piggin
> + * Copyright (C) 2007 Novell Inc.
> + */
> +#include <linux/sched.h>
> +#include <linux/mm.h>
> +#include <linux/vmstat.h>
> +#include <asm/pgtable.h>
> +
> +/*
> + * 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, result;
> + pte_t *ptep;
> +
> + result = _PAGE_PRESENT|_PAGE_USER;
> + if (write)
> + result |= _PAGE_RW;
> + mask = result | _PAGE_SPECIAL;
> +
> + ptep = pte_offset_map(&pmd, addr);
> + do {
> + /*
> + * XXX: careful. On 3-level 32-bit, the pte is 64 bits, and
> + * we need to make sure we load the low word first, then the
> + * high. This means _PAGE_PRESENT should be clear if the high
> + * word was not valid. Currently, the C compiler can issue
> + * the loads in any order, and I don't know of a wrapper
> + * function that will do this properly, so it is broken on
> + * 32-bit 3-level for the moment.
> + */
> + pte_t pte = *ptep;
> + struct page *page;
> +
> + if ((pte_val(pte) & mask) != result)
> + 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;
> +}
Would this be sufficient to address that comment's conern?
Index: linux-2.6/arch/x86/mm/gup.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/gup.c
+++ linux-2.6/arch/x86/mm/gup.c
@@ -36,8 +36,16 @@ static noinline int gup_pte_range(pmd_t
* function that will do this properly, so it is broken on
* 32-bit 3-level for the moment.
*/
- pte_t pte = *ptep;
struct page *page;
+ pte_t pte;
+
+#ifdef CONFIG_X86_PAE
+ pte.pte_low = ptep->pte_low;
+ barrier();
+ pte.pte_high = ptep->pte_high;
+#else
+ pte = *ptep;
+#endif
if ((pte_val(pte) & mask) != result)
return 0;
--
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