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[2003:cb:c702:6100:f5c9:50a5:3310:d8ac]) by smtp.gmail.com with ESMTPSA id m29-20020a05600c091d00b003dc521f336esm1824544wmp.14.2023.03.03.01.12.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 03 Mar 2023 01:12:27 -0800 (PST) Message-ID: <95b0a3dd-b6f9-0305-759c-b715359b0cab@redhat.com> Date: Fri, 3 Mar 2023 10:12:26 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH v1] mm/userfaultfd: propagate uffd-wp bit when PTE-mapping the huge zeropage To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Mike Rapoport , Andrea Arcangeli , Jerome Glisse , Shaohua Li References: <20230302175423.589164-1-david@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C4EBD140007 X-Stat-Signature: kwizw5b4p8arr553utg3q6y6hna1p61k X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1677834751-843674 X-HE-Meta: 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 ggaJEbww URAfOeNCqYVhqdJqIzs/igzE3FZW/xZjRNV8YiCxJnnX+IKXWojKlsCHdhIpdAd6jQillQ7P22v0o8V7Tps1FLqy2ZkwpuWLx3Z17kGQKyjAGwbB4ccjwCCGZRqGiTNqSLiPKGTLBlN92M7SeXDqqisjJMNTYUBg3tcXYsRR+lVEyLxwf+wbuUsfCam+Ifc22uBg/bSWYRmUuQm6TYx9uL7TirBWTtxGgPocO0mex30lYBa0c/B8C9Q4a53TMVlegtArdt2Amvc142Q/bBP7BmQrTto2dskqFiFjTdloaHy+RxQqMwyY1EAb2Ik3Uh5QhlYrQNu6Nj1OxyLDdPP04oOZ3UB5dgRuhW+qU3MyTXDoC7/Bhw0i4qsWyjVULUAUQHTI8MlvHRqt4xVaRb1fl3pZZuhzZmVU3SlCywqbTLlPVkBs= 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 02.03.23 23:29, Peter Xu wrote: > On Thu, Mar 02, 2023 at 06:54:23PM +0100, David Hildenbrand wrote: >> Currently, we'd lose the userfaultfd-wp marker when PTE-mapping a huge >> zeropage, resulting in the next write faults in the PMD range >> not triggering uffd-wp events. >> >> Various actions (partial MADV_DONTNEED, partial mremap, partial munmap, >> partial mprotect) could trigger this. However, most importantly, >> un-protecting a single sub-page from the userfaultfd-wp handler when >> processing a uffd-wp event will PTE-map the shared huge zeropage and >> lose the uffd-wp bit for the remainder of the PMD. >> >> Let's properly propagate the uffd-wp bit to the PMDs. > > Ouch.. I thought this was reported once, probably it fell through the > cracks. Yes, I reported it a while ago, but our understanding back then was that primarily MADV_DONTNEED would trigger it (which my reproducer back then did), and e.g., QEMU would make sure to not have concurrent MADV_DONTNEED while doing background snapshots. I realized only yesterday when retesting my patch that that a simple unprotect is already sufficient to mess it up. > > Acked-by: Peter Xu Thanks! -- Thanks, David / dhildenb