From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932446AbdKORdc (ORCPT ); Wed, 15 Nov 2017 12:33:32 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:42680 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753359AbdKORdZ (ORCPT ); Wed, 15 Nov 2017 12:33:25 -0500 Date: Wed, 15 Nov 2017 17:33:32 +0000 From: Will Deacon To: Michal Hocko Cc: Minchan Kim , Wang Nan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Bob Liu , Andrew Morton , David Rientjes , Ingo Molnar , Roman Gushchin , Konstantin Khlebnikov , Andrea Arcangeli Subject: Re: [PATCH] arch, mm: introduce arch_tlb_gather_mmu_lazy (was: Re: [RESEND PATCH] mm, oom_reaper: gather each vma to prevent) leaking TLB entry Message-ID: <20171115173332.GL19071@arm.com> References: <20171107095453.179940-1-wangnan0@huawei.com> <20171110001933.GA12421@bbox> <20171110101529.op6yaxtdke2p4bsh@dhcp22.suse.cz> <20171110122635.q26xdxytgdfjy5q3@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171110122635.q26xdxytgdfjy5q3@dhcp22.suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Michal, On Fri, Nov 10, 2017 at 01:26:35PM +0100, Michal Hocko wrote: > From 7f0fcd2cab379ddac5611b2a520cdca8a77a235b Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Fri, 10 Nov 2017 11:27:17 +0100 > Subject: [PATCH] arch, mm: introduce arch_tlb_gather_mmu_lazy > > 5a7862e83000 ("arm64: tlbflush: avoid flushing when fullmm == 1") has > introduced an optimization to not flush tlb when we are tearing the > whole address space down. Will goes on to explain > > : Basically, we tag each address space with an ASID (PCID on x86) which > : is resident in the TLB. This means we can elide TLB invalidation when > : pulling down a full mm because we won't ever assign that ASID to > : another mm without doing TLB invalidation elsewhere (which actually > : just nukes the whole TLB). > > This all is nice but tlb_gather users are not aware of that and this can > actually cause some real problems. E.g. the oom_reaper tries to reap the > whole address space but it might race with threads accessing the memory [1]. > It is possible that soft-dirty handling might suffer from the same > problem [2]. > > Introduce an explicit lazy variant tlb_gather_mmu_lazy which allows the > behavior arm64 implements for the fullmm case and replace it by an > explicit lazy flag in the mmu_gather structure. exit_mmap path is then > turned into the explicit lazy variant. Other architectures simply ignore > the flag. > > [1] http://lkml.kernel.org/r/20171106033651.172368-1-wangnan0@huawei.com > [2] http://lkml.kernel.org/r/20171110001933.GA12421@bbox > Signed-off-by: Michal Hocko > --- > arch/arm/include/asm/tlb.h | 3 ++- > arch/arm64/include/asm/tlb.h | 2 +- > arch/ia64/include/asm/tlb.h | 3 ++- > arch/s390/include/asm/tlb.h | 3 ++- > arch/sh/include/asm/tlb.h | 2 +- > arch/um/include/asm/tlb.h | 2 +- > include/asm-generic/tlb.h | 6 ++++-- > include/linux/mm_types.h | 2 ++ > mm/memory.c | 17 +++++++++++++++-- > mm/mmap.c | 2 +- > 10 files changed, 31 insertions(+), 11 deletions(-) > > diff --git a/arch/arm/include/asm/tlb.h b/arch/arm/include/asm/tlb.h > index d5562f9ce600..fe9042aee8e9 100644 > --- a/arch/arm/include/asm/tlb.h > +++ b/arch/arm/include/asm/tlb.h > @@ -149,7 +149,8 @@ static inline void tlb_flush_mmu(struct mmu_gather *tlb) > > static inline void > arch_tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, > - unsigned long start, unsigned long end) > + unsigned long start, unsigned long end, > + bool lazy) > { > tlb->mm = mm; > tlb->fullmm = !(start | (end+1)); > diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h > index ffdaea7954bb..7adde19b2bcc 100644 > --- a/arch/arm64/include/asm/tlb.h > +++ b/arch/arm64/include/asm/tlb.h > @@ -43,7 +43,7 @@ static inline void tlb_flush(struct mmu_gather *tlb) > * The ASID allocator will either invalidate the ASID or mark > * it as used. > */ > - if (tlb->fullmm) > + if (tlb->lazy) > return; This looks like the right idea, but I'd rather make this check: if (tlb->fullmm && tlb->lazy) since the optimisation doesn't work for anything than tearing down the entire address space. Alternatively, I could actually go check MMF_UNSTABLE in tlb->mm, which would save you having to add an extra flag in the first place, e.g.: if (tlb->fullmm && !test_bit(MMF_UNSTABLE, &tlb->mm->flags)) which is a nice one-liner. Will From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f70.google.com (mail-oi0-f70.google.com [209.85.218.70]) by kanga.kvack.org (Postfix) with ESMTP id 0BEA56B0033 for ; Wed, 15 Nov 2017 12:33:27 -0500 (EST) Received: by mail-oi0-f70.google.com with SMTP id o126so15468752oif.21 for ; Wed, 15 Nov 2017 09:33:27 -0800 (PST) Received: from foss.arm.com (usa-sjc-mx-foss1.foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id l95si8684132otl.339.2017.11.15.09.33.25 for ; Wed, 15 Nov 2017 09:33:25 -0800 (PST) Date: Wed, 15 Nov 2017 17:33:32 +0000 From: Will Deacon Subject: Re: [PATCH] arch, mm: introduce arch_tlb_gather_mmu_lazy (was: Re: [RESEND PATCH] mm, oom_reaper: gather each vma to prevent) leaking TLB entry Message-ID: <20171115173332.GL19071@arm.com> References: <20171107095453.179940-1-wangnan0@huawei.com> <20171110001933.GA12421@bbox> <20171110101529.op6yaxtdke2p4bsh@dhcp22.suse.cz> <20171110122635.q26xdxytgdfjy5q3@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171110122635.q26xdxytgdfjy5q3@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Minchan Kim , Wang Nan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Bob Liu , Andrew Morton , David Rientjes , Ingo Molnar , Roman Gushchin , Konstantin Khlebnikov , Andrea Arcangeli Hi Michal, On Fri, Nov 10, 2017 at 01:26:35PM +0100, Michal Hocko wrote: > From 7f0fcd2cab379ddac5611b2a520cdca8a77a235b Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Fri, 10 Nov 2017 11:27:17 +0100 > Subject: [PATCH] arch, mm: introduce arch_tlb_gather_mmu_lazy > > 5a7862e83000 ("arm64: tlbflush: avoid flushing when fullmm == 1") has > introduced an optimization to not flush tlb when we are tearing the > whole address space down. Will goes on to explain > > : Basically, we tag each address space with an ASID (PCID on x86) which > : is resident in the TLB. This means we can elide TLB invalidation when > : pulling down a full mm because we won't ever assign that ASID to > : another mm without doing TLB invalidation elsewhere (which actually > : just nukes the whole TLB). > > This all is nice but tlb_gather users are not aware of that and this can > actually cause some real problems. E.g. the oom_reaper tries to reap the > whole address space but it might race with threads accessing the memory [1]. > It is possible that soft-dirty handling might suffer from the same > problem [2]. > > Introduce an explicit lazy variant tlb_gather_mmu_lazy which allows the > behavior arm64 implements for the fullmm case and replace it by an > explicit lazy flag in the mmu_gather structure. exit_mmap path is then > turned into the explicit lazy variant. Other architectures simply ignore > the flag. > > [1] http://lkml.kernel.org/r/20171106033651.172368-1-wangnan0@huawei.com > [2] http://lkml.kernel.org/r/20171110001933.GA12421@bbox > Signed-off-by: Michal Hocko > --- > arch/arm/include/asm/tlb.h | 3 ++- > arch/arm64/include/asm/tlb.h | 2 +- > arch/ia64/include/asm/tlb.h | 3 ++- > arch/s390/include/asm/tlb.h | 3 ++- > arch/sh/include/asm/tlb.h | 2 +- > arch/um/include/asm/tlb.h | 2 +- > include/asm-generic/tlb.h | 6 ++++-- > include/linux/mm_types.h | 2 ++ > mm/memory.c | 17 +++++++++++++++-- > mm/mmap.c | 2 +- > 10 files changed, 31 insertions(+), 11 deletions(-) > > diff --git a/arch/arm/include/asm/tlb.h b/arch/arm/include/asm/tlb.h > index d5562f9ce600..fe9042aee8e9 100644 > --- a/arch/arm/include/asm/tlb.h > +++ b/arch/arm/include/asm/tlb.h > @@ -149,7 +149,8 @@ static inline void tlb_flush_mmu(struct mmu_gather *tlb) > > static inline void > arch_tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, > - unsigned long start, unsigned long end) > + unsigned long start, unsigned long end, > + bool lazy) > { > tlb->mm = mm; > tlb->fullmm = !(start | (end+1)); > diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h > index ffdaea7954bb..7adde19b2bcc 100644 > --- a/arch/arm64/include/asm/tlb.h > +++ b/arch/arm64/include/asm/tlb.h > @@ -43,7 +43,7 @@ static inline void tlb_flush(struct mmu_gather *tlb) > * The ASID allocator will either invalidate the ASID or mark > * it as used. > */ > - if (tlb->fullmm) > + if (tlb->lazy) > return; This looks like the right idea, but I'd rather make this check: if (tlb->fullmm && tlb->lazy) since the optimisation doesn't work for anything than tearing down the entire address space. Alternatively, I could actually go check MMF_UNSTABLE in tlb->mm, which would save you having to add an extra flag in the first place, e.g.: if (tlb->fullmm && !test_bit(MMF_UNSTABLE, &tlb->mm->flags)) which is a nice one-liner. Will -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org