On Thu 07-07-16 17:19:12, Dave Hansen wrote:
>
> From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>
> The erratum we are fixing here can lead to stray setting of the
> A and D bits. That means that a pte that we cleared might
> suddenly have A/D set. So, stop considering those bits when
> determining if a pte is pte_none(). The same goes for the
> other pmd_none() and pud_none(). pgd_none() can be skipped
> because it is not affected; we do not use PGD entries for
> anything other than pagetables on affected configurations.
>
> This adds a tiny amount of overhead to all pte_none() checks.
> I doubt we'll be able to measure it anywhere.
It would be better to introduce the overhead only for the affected
cpu models but I guess this is also acceptable. Would it be too
complicated to use alternatives for that?
> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Anyway
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
>
> b/arch/x86/include/asm/pgtable.h | 13 ++++++++++---
> b/arch/x86/include/asm/pgtable_types.h | 6 ++++++
> 2 files changed, 16 insertions(+), 3 deletions(-)
>
> diff -puN arch/x86/include/asm/pgtable.h~knl-strays-20-mod-pte-none arch/x86/include/asm/pgtable.h
> --- a/arch/x86/include/asm/pgtable.h~knl-strays-20-mod-pte-none 2016-07-07 17:17:43.974764976 -0700
> +++ b/arch/x86/include/asm/pgtable.h 2016-07-07 17:17:43.980765246 -0700
> @@ -480,7 +480,7 @@ pte_t *populate_extra_pte(unsigned long
>
> static inline int pte_none(pte_t pte)
> {
> - return !pte.pte;
> + return !(pte.pte & ~(_PAGE_KNL_ERRATUM_MASK));
> }
>
> #define __HAVE_ARCH_PTE_SAME
> @@ -552,7 +552,8 @@ static inline int pmd_none(pmd_t pmd)
> {
> /* Only check low word on 32-bit platforms, since it might be
> out of sync with upper half. */
> - return (unsigned long)native_pmd_val(pmd) == 0;
> + unsigned long val = native_pmd_val(pmd);
> + return (val & ~_PAGE_KNL_ERRATUM_MASK) == 0;
> }
>
> static inline unsigned long pmd_page_vaddr(pmd_t pmd)
> @@ -616,7 +617,7 @@ static inline unsigned long pages_to_mb(
> #if CONFIG_PGTABLE_LEVELS > 2
> static inline int pud_none(pud_t pud)
> {
> - return native_pud_val(pud) == 0;
> + return (native_pud_val(pud) & ~(_PAGE_KNL_ERRATUM_MASK)) == 0;
> }
>
> static inline int pud_present(pud_t pud)
> @@ -694,6 +695,12 @@ static inline int pgd_bad(pgd_t pgd)
>
> static inline int pgd_none(pgd_t pgd)
> {
> + /*
> + * There is no need to do a workaround for the KNL stray
> + * A/D bit erratum here. PGDs only point to page tables
> + * except on 32-bit non-PAE which is not supported on
> + * KNL.
> + */
> return !native_pgd_val(pgd);
> }
> #endif /* CONFIG_PGTABLE_LEVELS > 3 */
> diff -puN arch/x86/include/asm/pgtable_types.h~knl-strays-20-mod-pte-none arch/x86/include/asm/pgtable_types.h
> --- a/arch/x86/include/asm/pgtable_types.h~knl-strays-20-mod-pte-none 2016-07-07 17:17:43.976765066 -0700
> +++ b/arch/x86/include/asm/pgtable_types.h 2016-07-07 17:17:43.980765246 -0700
> @@ -70,6 +70,12 @@
> _PAGE_PKEY_BIT2 | \
> _PAGE_PKEY_BIT3)
>
> +#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
> +#define _PAGE_KNL_ERRATUM_MASK (_PAGE_DIRTY | _PAGE_ACCESSED)
> +#else
> +#define _PAGE_KNL_ERRATUM_MASK 0
> +#endif
> +
> #ifdef CONFIG_KMEMCHECK
> #define _PAGE_HIDDEN (_AT(pteval_t, 1) << _PAGE_BIT_HIDDEN)
> #else
> _
--
Michal Hocko
SUSE Labs
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>