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[174.89.135.171]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7e81542b0d3sm145980085a.21.2025.08.06.11.09.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 Aug 2025 11:09:35 -0700 (PDT) Date: Wed, 6 Aug 2025 14:09:32 -0400 From: Peter Xu To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, david@redhat.com, aarcange@redhat.com, lokeshgidra@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com, stable@vger.kernel.org Subject: Re: [PATCH v3 1/1] userfaultfd: fix a crash in UFFDIO_MOVE with some non-present PMDs Message-ID: References: <20250806154015.769024-1-surenb@google.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Y1JgZ5g0WaF_m_zPIToF3pPUwvnApUKXWJFp61hsZ5o_1754503776 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 2E754C000D X-Stat-Signature: ypba47qraehgeqmfbq9kb6m8hpdqpgns X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1754503779-572817 X-HE-Meta: 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 brZRU48z 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 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: List-Subscribe: List-Unsubscribe: On Wed, Aug 06, 2025 at 10:09:30AM -0700, Suren Baghdasaryan wrote: > On Wed, Aug 6, 2025 at 9:56 AM Peter Xu wrote: > > > > On Wed, Aug 06, 2025 at 08:40:15AM -0700, Suren Baghdasaryan wrote: > > > When UFFDIO_MOVE is used with UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES and it > > > > The migration entry can appear with/without ALLOW_SRC_HOLES, right? Maybe > > drop this line? > > Yes, you are right. I'll update. > > > > > If we need another repost, the subject can further be tailored to mention > > migration entry too rather than non-present. IMHO that's clearer on > > explaining the issue this patch is fixing (e.g. a valid transhuge THP can > > also have present bit cleared). > > > > > encounters a non-present PMD (migration entry), it proceeds with folio > > > access even though the folio is not present. Add the missing check and > > > > IMHO "... even though folio is not present" is pretty vague. Maybe > > "... even though it's a swap entry"? Fundamentally it's because of the > > different layouts of normal THP v.s. a swap entry, hence pmd_folio() should > > not be used on top of swap entries. > > Well, technically a migration entry is a non_swap_entry(), so calling > migration entries "swap entries" is confusing to me. Any better > wording we can use or do you think that's ok? The more general definition of "swap entry" should follow what swp_entry_t is defined, where, for example, is_migration_entry() itself takes swp_entry_t as input. So it should be fine, but I agree it's indeed confusing. If we want to make it clearer, IMHO we could rename non_swap_entry() instead to is_swapfile_entry() / is_real_swap_entry() / ... but that can be discussed separately. Here, if we want to make it super accurate, we could also use "swp_entry_t" instead of "swap entry", that'll be 100% accurate. Thanks, -- Peter Xu