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[70.52.228.144]) by smtp.gmail.com with ESMTPSA id gc11-20020a05622a59cb00b003a50d92f9b4sm22226580qtb.1.2023.01.05.12.00.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Jan 2023 12:00:25 -0800 (PST) Date: Thu, 5 Jan 2023 15:00:23 -0500 From: Peter Xu To: James Houghton Cc: Mike Kravetz , Muchun Song , Axel Rasmussen , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] hugetlb: unshare some PMDs when splitting VMAs Message-ID: References: <20230104231910.1464197-1-jthoughton@google.com> MIME-Version: 1.0 In-Reply-To: <20230104231910.1464197-1-jthoughton@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: 87850C002D X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: isjcdhnq5rkuuowdw8f4cs1e1zkzodpg X-HE-Tag: 1672948828-935137 X-HE-Meta: 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 Ku14AE3k DGujZvLi6YZ86fnlpvsK6KSH9ddqDdylZxPI1x1TI5c5FLEIAZfY/IeO4pOR2lQ3MMah1+qKWp9l5vKdd26LFFd4kYbNIYzHGSYtK/5xTBysCWPE= 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 Wed, Jan 04, 2023 at 11:19:10PM +0000, James Houghton wrote: > PMD sharing can only be done in PUD_SIZE-aligned pieces of VMAs; > however, it is possible that HugeTLB VMAs are split without unsharing > the PMDs first. > > Without this fix, it is possible to hit the uffd-wp-related WARN_ON_ONCE > in hugetlb_change_protection [1]. The key there is that > hugetlb_unshare_all_pmds will not attempt to unshare PMDs in > non-PUD_SIZE-aligned sections of the VMA. > > It might seem ideal to unshare in hugetlb_vm_op_open, but we need to > unshare in both the new and old VMAs, so unsharing in > hugetlb_vm_op_split seems natural. > > [1]: https://lore.kernel.org/linux-mm/CADrL8HVeOkj0QH5VZZbRzybNE8CG-tEGFshnA+bG9nMgcWtBSg@mail.gmail.com/ > > Fixes: 6dfeaff93be1 ("hugetlb/userfaultfd: unshare all pmds for hugetlbfs when register wp") > Signed-off-by: James Houghton Acked-by: Peter Xu Thanks, -- Peter Xu