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[174.95.95.253]) by smtp.gmail.com with ESMTPSA id z65sm15976988qtd.15.2021.03.03.11.03.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Mar 2021 11:03:28 -0800 (PST) Date: Wed, 3 Mar 2021 14:03:27 -0500 From: Peter Xu To: Nadav Amit Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Nadav Amit , Andrea Arcangeli , Andy Lutomirski , Pavel Emelyanov , Mike Kravetz , Mike Rapoport , Minchan Kim , Will Deacon , Peter Zijlstra , stable@vger.kernel.org, Yu Zhao Subject: Re: [PATCH RESEND v3] mm/userfaultfd: fix memory corruption due to writeprotect Message-ID: <20210303190327.GV397383@xz-x1> References: <20210303095702.3814618-1-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210303095702.3814618-1-namit@vmware.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 03, 2021 at 01:57:02AM -0800, Nadav Amit wrote: > From: Nadav Amit > > Userfaultfd self-test fails occasionally, indicating a memory > corruption. It's failing very constantly now for me after I got it run on a 40 cores system... While indeed not easy to fail on my laptop. [...] > Fixes: 292924b26024 ("userfaultfd: wp: apply _PAGE_UFFD_WP bit") > Signed-off-by: Nadav Amit > > --- > v2->v3: > * Do not acquire mmap_lock for write, flush conditionally instead [Yu] > * Change the fixes tag to the patch that made the race apparent [Yu] Did you forget about this one? It would still be good to point to 09854ba94c6a just to show that 5.7/5.8 stable branches shouldn't need this patch as they're not prone to the tlb data curruption. Maybe also cc stable with 5.9+? > * Removing patch to avoid write-protect on uffd unprotect. More > comprehensive solution to follow (and avoid the TLB flush as well). > --- > mm/memory.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/mm/memory.c b/mm/memory.c > index 9e8576a83147..06da04f98936 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3092,6 +3092,13 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) > return handle_userfault(vmf, VM_UFFD_WP); > } > > + /* > + * Userfaultfd write-protect can defer flushes. Ensure the TLB > + * is flushed in this case before copying. > + */ > + if (userfaultfd_wp(vmf->vma) && mm_tlb_flush_pending(vmf->vma->vm_mm)) > + flush_tlb_page(vmf->vma, vmf->address); > + > vmf->page = vm_normal_page(vma, vmf->address, vmf->orig_pte); > if (!vmf->page) { > /* > -- > 2.25.1 > Thanks for being consistent on fixing this problem. Maybe it's even better to put that into a "unlikely" to reduce the affect of normal do_wp_page as much as possible? But I'll leave it to others. If with the fixes tag modified: Reviewed-by: Peter Xu Tested-by: Peter Xu Thanks, -- Peter Xu