Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932495Ab1BPAZ7 (ORCPT ); Tue, 15 Feb 2011 19:25:59 -0500 Received: from kroah.org ([198.145.64.141]:49938 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932483Ab1BPAZf (ORCPT ); Tue, 15 Feb 2011 19:25:35 -0500 X-Mailbox-Line: From gregkh@clark.kroah.org Tue Feb 15 16:14:51 2011 Message-Id: <20110216001451.473222737@clark.kroah.org> User-Agent: quilt/0.48-11.2 Date: Tue, 15 Feb 2011 16:15:21 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Suresh Siddha , Ingo Molnar Subject: [264/272] x86, mm: avoid possible bogus tlb entries by clearing prev mm_cpumask after switching mm In-Reply-To: <20110216001559.GA31413@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3115 Lines: 81 2.6.37-stable review patch. If anyone has any objections, please let us know. ------------------ From: Suresh Siddha commit 831d52bc153971b70e64eccfbed2b232394f22f8 upstream. Clearing the cpu in prev's mm_cpumask early will avoid the flush tlb IPI's while the cr3 is still pointing to the prev mm. And this window can lead to the possibility of bogus TLB fills resulting in strange failures. One such problematic scenario is mentioned below. T1. CPU-1 is context switching from mm1 to mm2 context and got a NMI etc between the point of clearing the cpu from the mm_cpumask(mm1) and before reloading the cr3 with the new mm2. T2. CPU-2 is tearing down a specific vma for mm1 and will proceed with flushing the TLB for mm1. It doesn't send the flush TLB to CPU-1 as it doesn't see that cpu listed in the mm_cpumask(mm1). T3. After the TLB flush is complete, CPU-2 goes ahead and frees the page-table pages associated with the removed vma mapping. T4. CPU-2 now allocates those freed page-table pages for something else. T5. As the CR3 and TLB caches for mm1 is still active on CPU-1, CPU-1 can potentially speculate and walk through the page-table caches and can insert new TLB entries. As the page-table pages are already freed and being used on CPU-2, this page walk can potentially insert a bogus global TLB entry depending on the (random) contents of the page that is being used on CPU-2. T6. This bogus TLB entry being global will be active across future CR3 changes and can result in weird memory corruption etc. To avoid this issue, for the prev mm that is handing over the cpu to another mm, clear the cpu from the mm_cpumask(prev) after the cr3 is changed. Marking it for -stable, though we haven't seen any reported failure that can be attributed to this. Signed-off-by: Suresh Siddha Acked-by: Ingo Molnar Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/mmu_context.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -36,8 +36,6 @@ static inline void switch_mm(struct mm_s unsigned cpu = smp_processor_id(); if (likely(prev != next)) { - /* stop flush ipis for the previous mm */ - cpumask_clear_cpu(cpu, mm_cpumask(prev)); #ifdef CONFIG_SMP percpu_write(cpu_tlbstate.state, TLBSTATE_OK); percpu_write(cpu_tlbstate.active_mm, next); @@ -47,6 +45,9 @@ static inline void switch_mm(struct mm_s /* Re-load page tables */ load_cr3(next->pgd); + /* stop flush ipis for the previous mm */ + cpumask_clear_cpu(cpu, mm_cpumask(prev)); + /* * load the LDT, if the LDT is different: */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/