From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e28smtp08.in.ibm.com (e28smtp08.in.ibm.com [122.248.162.8]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e28smtp08.in.ibm.com", Issuer "GeoTrust SSL CA" (not verified)) by ozlabs.org (Postfix) with ESMTPS id 336BA2C00A2 for ; Thu, 23 May 2013 02:58:28 +1000 (EST) Received: from /spool/local by e28smtp08.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 22 May 2013 22:21:10 +0530 Received: from d28relay05.in.ibm.com (d28relay05.in.ibm.com [9.184.220.62]) by d28dlp02.in.ibm.com (Postfix) with ESMTP id 3654A394004E for ; Wed, 22 May 2013 22:28:23 +0530 (IST) Received: from d28av03.in.ibm.com (d28av03.in.ibm.com [9.184.220.65]) by d28relay05.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r4MGwGaQ11010376 for ; Wed, 22 May 2013 22:28:16 +0530 Received: from d28av03.in.ibm.com (loopback [127.0.0.1]) by d28av03.in.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r4MGwKRS020695 for ; Thu, 23 May 2013 02:58:21 +1000 From: "Aneesh Kumar K.V" To: benh@kernel.crashing.org, paulus@samba.org, dwg@au1.ibm.com Subject: [PATCH -V9 15/20] powerpc: Prevent gcc to re-read the pagetables Date: Wed, 22 May 2013 22:27:47 +0530 Message-Id: <1369241872-15700-16-git-send-email-aneesh.kumar@linux.vnet.ibm.com> In-Reply-To: <1369241872-15700-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> References: <1369241872-15700-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> Cc: linuxppc-dev@lists.ozlabs.org, "Aneesh Kumar K.V" List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: "Aneesh Kumar K.V" GCC is very likely to read the pagetables just once and cache them in the local stack or in a register, but it is can also decide to re-read the pagetables. The problem is that the pagetable in those places can change from under gcc. With THP/hugetlbfs the pmd (and pgd for hugetlbfs giga pages) can change under gup_fast. The pages won't be freed untill we finish gup fast because we have irq disabled and we free these pages via rcu callback. Signed-off-by: Aneesh Kumar K.V --- arch/powerpc/mm/gup.c | 8 ++++---- arch/powerpc/mm/hugetlbpage.c | 2 +- 2 files changed, 5 insertions(+), 5 deletions(-) diff --git a/arch/powerpc/mm/gup.c b/arch/powerpc/mm/gup.c index 3d36fd7..4823e4d 100644 --- a/arch/powerpc/mm/gup.c +++ b/arch/powerpc/mm/gup.c @@ -34,7 +34,7 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr, ptep = pte_offset_kernel(&pmd, addr); do { - pte_t pte = *ptep; + pte_t pte = ACCESS_ONCE(*ptep); struct page *page; if ((pte_val(pte) & mask) != result) @@ -63,7 +63,7 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, pmdp = pmd_offset(&pud, addr); do { - pmd_t pmd = *pmdp; + pmd_t pmd = ACCESS_ONCE(*pmdp); next = pmd_addr_end(addr, end); /* @@ -102,7 +102,7 @@ static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end, pudp = pud_offset(&pgd, addr); do { - pud_t pud = *pudp; + pud_t pud = ACCESS_ONCE(*pudp); next = pud_addr_end(addr, end); if (pud_none(pud)) @@ -165,7 +165,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write, pgdp = pgd_offset(mm, addr); do { - pgd_t pgd = *pgdp; + pgd_t pgd = ACCESS_ONCE(*pgdp); pr_devel(" %016lx: normal pgd %p\n", addr, (void *)pgd_val(pgd)); diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c index e9e6882..f2f01fd 100644 --- a/arch/powerpc/mm/hugetlbpage.c +++ b/arch/powerpc/mm/hugetlbpage.c @@ -1024,7 +1024,7 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, if (pte_end < end) end = pte_end; - pte = *ptep; + pte = ACCESS_ONCE(*ptep); mask = _PAGE_PRESENT | _PAGE_USER; if (write) mask |= _PAGE_RW; -- 1.8.1.2