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[70.52.229.124]) by smtp.gmail.com with ESMTPSA id 77-20020a370650000000b007458c5a807csm9774944qkg.83.2023.03.21.12.25.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Mar 2023 12:25:28 -0700 (PDT) Date: Tue, 21 Mar 2023 15:25:26 -0400 From: Peter Xu To: Muhammad Usama Anjum Cc: David Hildenbrand , Andrew Morton , =?utf-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , Andrei Vagin , Danylo Mocherniuk , Paul Gofman , Cyrill Gorcunov , Mike Rapoport , Nadav Amit , Alexander Viro , Shuah Khan , Christian Brauner , Yang Shi , Vlastimil Babka , "Liam R . Howlett" , Yun Zhou , Suren Baghdasaryan , Alex Sierra , Matthew Wilcox , Pasha Tatashin , Axel Rasmussen , "Gustavo A . R . Silva" , Dan Williams , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Greg KH , kernel@collabora.com Subject: Re: [PATCH v11 1/7] userfaultfd: Add UFFD WP Async support Message-ID: References: <20230309135718.1490461-1-usama.anjum@collabora.com> <20230309135718.1490461-2-usama.anjum@collabora.com> <1b78ee32-003d-5645-c223-619b66d41733@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1b78ee32-003d-5645-c223-619b66d41733@collabora.com> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hi, Muhammad, On Tue, Mar 21, 2023 at 05:21:15PM +0500, Muhammad Usama Anjum wrote: > Thank you so much for the patch. I've tested hugetlb mem. This patch is > working fine for hugetlb shmem: > *shmid = shmget(2, size, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W); > mem = shmat(*shmid, 0, 0); > > I've found slight issue with hugetlb mem which has been mmaped: > mem = mmap(NULL, size, PROT_READ | PROT_WRITE, > MAP_ANONYMOUS | MAP_HUGETLB | MAP_PRIVATE, -1, 0); > The issue is that even after witting to this memory, the wp flag is still > present there and memory doesn't appear to be dirty when it should have > been dirty. The temporary fix is to write to memory and write protect the > memory one extra time. I looked into this today and found it's an existing bug that can trigger with sync mode too.. as long as protection applied to unpopulated hugetlb private mappings, then write to it. I've sent a fix for it here and have you copied: https://lore.kernel.org/linux-mm/20230321191840.1897940-1-peterx@redhat.com/T/#u Please have a look and see whether it also fixes your issue. PS: recently I added a warning in commit c2da319c2e2789 and that can indeed capture this one when verifying using pagemap. I'd guess your dmesg should also contain something dumped. Thanks, -- Peter Xu