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[115.124.30.56]) by mx.google.com with ESMTPS id g10si3957806pgs.397.2019.05.09.11.36.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 09 May 2019 11:36:03 -0700 (PDT) Received-SPF: pass (google.com: domain of yang.shi@linux.alibaba.com designates 115.124.30.56 as permitted sender) client-ip=115.124.30.56; Authentication-Results: mx.google.com; spf=pass (google.com: domain of yang.shi@linux.alibaba.com designates 115.124.30.56 as permitted sender) smtp.mailfrom=yang.shi@linux.alibaba.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=alibaba.com X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R211e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04400;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0TRHO45d_1557426956; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TRHO45d_1557426956) by smtp.aliyun-inc.com(127.0.0.1); Fri, 10 May 2019 02:36:00 +0800 Subject: Re: [PATCH] mm: mmu_gather: remove __tlb_reset_range() for force flush To: Peter Zijlstra , Will Deacon Cc: jstancek@redhat.com, akpm@linux-foundation.org, stable@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, aneesh.kumar@linux.vnet.ibm.com, npiggin@gmail.com, namit@vmware.com, minchan@kernel.org, Mel Gorman References: <1557264889-109594-1-git-send-email-yang.shi@linux.alibaba.com> <20190509083726.GA2209@brain-police> <20190509103813.GP2589@hirez.programming.kicks-ass.net> <20190509105446.GL2650@hirez.programming.kicks-ass.net> From: Yang Shi Message-ID: <6a907073-67ec-04fe-aaae-c1adcb62e3df@linux.alibaba.com> Date: Thu, 9 May 2019 11:35:55 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20190509105446.GL2650@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 5/9/19 3:54 AM, Peter Zijlstra wrote: > On Thu, May 09, 2019 at 12:38:13PM +0200, Peter Zijlstra wrote: > >> That's tlb->cleared_p*, and yes agreed. That is, right until some >> architecture has level dependent TLBI instructions, at which point we'll >> need to have them all set instead of cleared. >> Anyway; am I correct in understanding that the actual problem is that >> we've cleared freed_tables and the ARM64 tlb_flush() will then not >> invalidate the cache and badness happens? >> >> Because so far nobody has actually provided a coherent description of >> the actual problem we're trying to solve. But I'm thinking something >> like the below ought to do. > There's another 'fun' issue I think. For architectures like ARM that > have range invalidation and care about VM_EXEC for I$ invalidation, the > below doesn't quite work right either. > > I suspect we also have to force: tlb->vma_exec = 1. Isn't the below code in tlb_flush enough to guarantee this? ... } else if (tlb->end) {                struct vm_area_struct vma = {                        .vm_mm = tlb->mm,                        .vm_flags = (tlb->vma_exec ? VM_EXEC    : 0) |                                    (tlb->vma_huge ? VM_HUGETLB : 0),                }; ... > > And I don't think there's an architecture that cares, but depending on > details I can construct cases where any setting of tlb->vm_hugetlb is > wrong, so that is _awesome_. But I suspect the sane thing for now is to > force it 0. > >> diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c >> index 99740e1dd273..fe768f8d612e 100644 >> --- a/mm/mmu_gather.c >> +++ b/mm/mmu_gather.c >> @@ -244,15 +244,20 @@ void tlb_finish_mmu(struct mmu_gather *tlb, >> unsigned long start, unsigned long end) >> { >> /* >> - * If there are parallel threads are doing PTE changes on same range >> - * under non-exclusive lock(e.g., mmap_sem read-side) but defer TLB >> - * flush by batching, a thread has stable TLB entry can fail to flush >> - * the TLB by observing pte_none|!pte_dirty, for example so flush TLB >> - * forcefully if we detect parallel PTE batching threads. >> + * Sensible comment goes here.. >> */ >> - if (mm_tlb_flush_nested(tlb->mm)) { >> - __tlb_reset_range(tlb); >> - __tlb_adjust_range(tlb, start, end - start); >> + if (mm_tlb_flush_nested(tlb->mm) && !tlb->full_mm) { >> + /* >> + * Since we're can't tell what we actually should have >> + * flushed flush everything in the given range. >> + */ >> + tlb->start = start; >> + tlb->end = end; >> + tlb->freed_tables = 1; >> + tlb->cleared_ptes = 1; >> + tlb->cleared_pmds = 1; >> + tlb->cleared_puds = 1; >> + tlb->cleared_p4ds = 1; >> } >> >> tlb_flush_mmu(tlb);