From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751253AbcGMPWD (ORCPT ); Wed, 13 Jul 2016 11:22:03 -0400 Received: from mail-wm0-f41.google.com ([74.125.82.41]:35288 "EHLO mail-wm0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750854AbcGMPVy (ORCPT ); Wed, 13 Jul 2016 11:21:54 -0400 Date: Wed, 13 Jul 2016 17:21:45 +0200 From: Michal Hocko To: Dave Hansen 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() Message-ID: <20160713152145.GC20693@dhcp22.suse.cz> References: <20160708001909.FB2443E2@viggo.jf.intel.com> <20160708001912.5216F89C@viggo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160708001912.5216F89C@viggo.jf.intel.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 07-07-16 17:19:12, Dave Hansen wrote: > > From: Dave Hansen > > 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 Anyway Acked-by: Michal Hocko > --- > > 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