From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id BBB7A6B0253 for ; Wed, 13 Jul 2016 11:23:31 -0400 (EDT) Received: by mail-wm0-f71.google.com with SMTP id f126so38050694wma.3 for ; Wed, 13 Jul 2016 08:23:31 -0700 (PDT) Received: from mail2-relais-roc.national.inria.fr (mail2-relais-roc.national.inria.fr. [192.134.164.83]) by mx.google.com with ESMTPS id dc8si1586812wjb.44.2016.07.13.08.23.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 13 Jul 2016 08:23:30 -0700 (PDT) Date: Wed, 13 Jul 2016 17:23:27 +0200 (CEST) From: Julia Lawall Subject: Re: [PATCH 4/4] x86: use pte_none() to test for empty PTE In-Reply-To: <20160713151820.GA20693@dhcp22.suse.cz> Message-ID: References: <20160708001909.FB2443E2@viggo.jf.intel.com> <20160708001915.813703D9@viggo.jf.intel.com> <20160713151820.GA20693@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Dave Hansen , 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 On Wed, 13 Jul 2016, Michal Hocko wrote: > [CCing Julia] > > On Thu 07-07-16 17:19:15, Dave Hansen wrote: > > > > From: Dave Hansen > > > > The page table manipulation code seems to have grown a couple of > > sites that are looking for empty PTEs. Just in case one of these > > entries got a stray bit set, use pte_none() instead of checking > > for a zero pte_val(). > > This looks like something that coccinelle could help with and automate. > Especially when the patch seems interesting for applying to older kernel > code streams. > > Julia would it be hard to generate a metapatch which would check the > {pte,pmd}_val() usage in conditions and replace them with {pte,pmd}_none > equivalents? Thanks for forwarding. A priori, it looks quite trivial. I will do the obvious thing and send the results for verification. julia > > The use pte_same() makes me a bit nervous. If we were doing a > > pte_same() check against two cleared entries and one of them had > > a stray bit set, it might fail the pte_same() check. But, I > > don't think we ever _do_ pte_same() for cleared entries. It is > > almost entirely used for checking for races in fault-in paths. > > > > Signed-off-by: Dave Hansen > > Other than that looks good to me. Feel free to add > Acked-by: Michal Hocko > > > --- > > > > b/arch/x86/mm/init_64.c | 12 ++++++------ > > b/arch/x86/mm/pageattr.c | 2 +- > > b/arch/x86/mm/pgtable_32.c | 2 +- > > 3 files changed, 8 insertions(+), 8 deletions(-) > > > > diff -puN arch/x86/mm/init_64.c~knl-strays-50-pte_val-cleanups arch/x86/mm/init_64.c > > --- a/arch/x86/mm/init_64.c~knl-strays-50-pte_val-cleanups 2016-07-07 17:17:44.942808493 -0700 > > +++ b/arch/x86/mm/init_64.c 2016-07-07 17:17:44.949808807 -0700 > > @@ -354,7 +354,7 @@ phys_pte_init(pte_t *pte_page, unsigned > > * pagetable pages as RO. So assume someone who pre-setup > > * these mappings are more intelligent. > > */ > > - if (pte_val(*pte)) { > > + if (!pte_none(*pte)) { > > if (!after_bootmem) > > pages++; > > continue; > > @@ -396,7 +396,7 @@ phys_pmd_init(pmd_t *pmd_page, unsigned > > continue; > > } > > > > - if (pmd_val(*pmd)) { > > + if (!pmd_none(*pmd)) { > > if (!pmd_large(*pmd)) { > > spin_lock(&init_mm.page_table_lock); > > pte = (pte_t *)pmd_page_vaddr(*pmd); > > @@ -470,7 +470,7 @@ phys_pud_init(pud_t *pud_page, unsigned > > continue; > > } > > > > - if (pud_val(*pud)) { > > + if (!pud_none(*pud)) { > > if (!pud_large(*pud)) { > > pmd = pmd_offset(pud, 0); > > last_map_addr = phys_pmd_init(pmd, addr, end, > > @@ -673,7 +673,7 @@ static void __meminit free_pte_table(pte > > > > for (i = 0; i < PTRS_PER_PTE; i++) { > > pte = pte_start + i; > > - if (pte_val(*pte)) > > + if (!pte_none(*pte)) > > return; > > } > > > > @@ -691,7 +691,7 @@ static void __meminit free_pmd_table(pmd > > > > for (i = 0; i < PTRS_PER_PMD; i++) { > > pmd = pmd_start + i; > > - if (pmd_val(*pmd)) > > + if (!pmd_none(*pmd)) > > return; > > } > > > > @@ -710,7 +710,7 @@ static bool __meminit free_pud_table(pud > > > > for (i = 0; i < PTRS_PER_PUD; i++) { > > pud = pud_start + i; > > - if (pud_val(*pud)) > > + if (!pud_none(*pud)) > > return false; > > } > > > > diff -puN arch/x86/mm/pageattr.c~knl-strays-50-pte_val-cleanups arch/x86/mm/pageattr.c > > --- a/arch/x86/mm/pageattr.c~knl-strays-50-pte_val-cleanups 2016-07-07 17:17:44.944808582 -0700 > > +++ b/arch/x86/mm/pageattr.c 2016-07-07 17:17:44.950808852 -0700 > > @@ -1185,7 +1185,7 @@ repeat: > > return __cpa_process_fault(cpa, address, primary); > > > > old_pte = *kpte; > > - if (!pte_val(old_pte)) > > + if (pte_none(old_pte)) > > return __cpa_process_fault(cpa, address, primary); > > > > if (level == PG_LEVEL_4K) { > > diff -puN arch/x86/mm/pgtable_32.c~knl-strays-50-pte_val-cleanups arch/x86/mm/pgtable_32.c > > --- a/arch/x86/mm/pgtable_32.c~knl-strays-50-pte_val-cleanups 2016-07-07 17:17:44.946808672 -0700 > > +++ b/arch/x86/mm/pgtable_32.c 2016-07-07 17:17:44.950808852 -0700 > > @@ -47,7 +47,7 @@ void set_pte_vaddr(unsigned long vaddr, > > return; > > } > > pte = pte_offset_kernel(pmd, vaddr); > > - if (pte_val(pteval)) > > + if (!pte_none(pteval)) > > set_pte_at(&init_mm, vaddr, pte, pteval); > > else > > pte_clear(&init_mm, vaddr, pte); > > _ > > -- > Michal Hocko > SUSE Labs > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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