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[99.254.114.190]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-72d4067f84csm9648975b3a.142.2025.01.15.09.21.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jan 2025 09:21:20 -0800 (PST) Date: Wed, 15 Jan 2025 12:21:15 -0500 From: Peter Xu To: Ryan Roberts Cc: Andrew Morton , Muchun Song , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Shuah Khan , David Hildenbrand , =?utf-8?Q?Miko=C5=82aj?= Lenczewski , Mark Rutland , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v1 1/2] mm: Clear uffd-wp PTE/PMD state on mremap() Message-ID: References: <20250107144755.1871363-1-ryan.roberts@arm.com> <20250107144755.1871363-2-ryan.roberts@arm.com> <26ee9ae0-405f-4085-a864-48d1ee6371f1@arm.com> MIME-Version: 1.0 In-Reply-To: <26ee9ae0-405f-4085-a864-48d1ee6371f1@arm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: doZIoH-Uum_6ASNayBLrvLPneceV6WvN3kaYeJ7tMD4_1736961682 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: A1DAD1C001D X-Stat-Signature: 9q7jy46ssgjfpbjjmtoh7a79dej3hjhp X-HE-Tag: 1736961684-551917 X-HE-Meta: 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 jhEombDn BxhulxmKXaY6Mh9CjEaGoGORhjRM41/ffWdKVq2uhfWeLVUZ6mT/qB3e+LScuioIu606FGx08a6yHj2ahFQJREimy+Vcm0AoEKpSU/y88ifyanwQ2DAUIwv0J7nUXR8EzlNTHJz9hkeRIfmzlXOUg7AJyjX8vt4jLHQVQnmLF9eS7WDzjPuQCO7MfoVmndrj1IUINgUS9t0KzigEChG+M9EAzJpwDYja8BRGTJEcE86VSNukIMiypQZDqwd6gCxKGbsLWw3lF5b8FEoQ4ANzCqMiTbEpSDrL3KL1VwjAIZkKeIl8PJRSeidaL1zNOSj94Ur6PdmyBA/97zLoMFktnZq3mOYkFPW3XL7BmXbnv3ssTgUYicb8Y/3wjdQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jan 15, 2025 at 04:58:06PM +0000, Ryan Roberts wrote: > Hi Peter, David, Hey, Ryan, > > On 07/01/2025 14:47, Ryan Roberts wrote: > > When mremap()ing a memory region previously registered with userfaultfd > > as write-protected but without UFFD_FEATURE_EVENT_REMAP, an > > inconsistency in flag clearing leads to a mismatch between the vma flags > > (which have uffd-wp cleared) and the pte/pmd flags (which do not have > > uffd-wp cleared). This mismatch causes a subsequent mprotect(PROT_WRITE) > > to trigger a warning in page_table_check_pte_flags() due to setting the > > pte to writable while uffd-wp is still set. > > > > Fix this by always explicitly clearing the uffd-wp pte/pmd flags on any > > such mremap() so that the values are consistent with the existing > > clearing of VM_UFFD_WP. Be careful to clear the logical flag regardless > > of its physical form; a PTE bit, a swap PTE bit, or a PTE marker. Cover > > PTE, huge PMD and hugetlb paths. > > I just noticed that Andrew sent this to Linus and it's now in his tree; I'm > suddenly very nervous that it doesn't have any acks. I don't suppose you would > be able to do a quick review to calm the nerves?? Heh, I fully trusted you, and I appreciated your help too. I'll need to run for 1-2 hours, but I'll read it this afternoon. Side note: no review is as good as tests on reliability POV if that was the concern, but I'll try my best. Thanks, -- Peter Xu