From: Michal Hocko <mhocko@kernel.org>
To: Dave Hansen <dave@sr71.net>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org,
torvalds@linux-foundation.org, akpm@linux-foundation.org,
bp@alien8.de, ak@linux.intel.com, dave.hansen@intel.com,
dave.hansen@linux.intel.com
Subject: Re: [PATCH 2/4] x86, pagetable: ignore A/D bits in pte/pmd/pud_none()
Date: Wed, 13 Jul 2016 17:21:45 +0200 [thread overview]
Message-ID: <20160713152145.GC20693@dhcp22.suse.cz> (raw)
In-Reply-To: <20160708001912.5216F89C@viggo.jf.intel.com>
On Thu 07-07-16 17:19:12, Dave Hansen wrote:
>
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> 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@linux.intel.com>
Anyway
Acked-by: Michal Hocko <mhocko@suse.com>
> ---
>
> 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
next prev parent reply other threads:[~2016-07-13 15:22 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-08 0:19 [PATCH 0/4] [RFC][v4] Workaround for Xeon Phi PTE A/D bits erratum Dave Hansen
2016-07-08 0:19 ` [PATCH 1/4] x86, swap: move swap offset/type up in PTE to work around erratum Dave Hansen
2016-07-13 8:03 ` [tip:x86/mm] x86/mm: Move " tip-bot for Dave Hansen
2016-07-13 15:19 ` [PATCH 1/4] x86, swap: move " Michal Hocko
2016-07-08 0:19 ` [PATCH 2/4] x86, pagetable: ignore A/D bits in pte/pmd/pud_none() Dave Hansen
2016-07-13 8:03 ` [tip:x86/mm] x86/mm: Ignore " tip-bot for Dave Hansen
2016-07-13 15:21 ` Michal Hocko [this message]
2016-07-13 15:47 ` [PATCH 2/4] x86, pagetable: ignore " Dave Hansen
2016-07-14 6:13 ` Michal Hocko
2016-07-08 0:19 ` [PATCH 3/4] x86: disallow running with 32-bit PTEs to work around erratum Dave Hansen
2016-07-13 8:04 ` [tip:x86/mm] x86/mm: Disallow " tip-bot for Dave Hansen
2016-07-08 0:19 ` [PATCH 4/4] x86: use pte_none() to test for empty PTE Dave Hansen
2016-07-13 8:04 ` [tip:x86/mm] x86/mm: Use " tip-bot for Dave Hansen
2016-07-13 15:18 ` [PATCH 4/4] x86: use " Michal Hocko
2016-07-13 15:23 ` Julia Lawall
2016-07-13 15:49 ` Julia Lawall
2016-07-13 16:28 ` Dave Hansen
2016-07-14 13:47 ` Vlastimil Babka
2016-07-14 14:24 ` Dave Hansen
2016-07-14 14:50 ` David Vrabel
2016-07-13 9:54 ` [PATCH 0/4] [RFC][v4] Workaround for Xeon Phi PTE A/D bits erratum Vlastimil Babka
-- strict thread matches above, loose matches on Subject: below --
2016-07-01 17:46 Dave Hansen
2016-07-01 17:47 ` [PATCH 2/4] x86, pagetable: ignore A/D bits in pte/pmd/pud_none() Dave Hansen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160713152145.GC20693@dhcp22.suse.cz \
--to=mhocko@kernel.org \
--cc=ak@linux.intel.com \
--cc=akpm@linux-foundation.org \
--cc=bp@alien8.de \
--cc=dave.hansen@intel.com \
--cc=dave.hansen@linux.intel.com \
--cc=dave@sr71.net \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=torvalds@linux-foundation.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).