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[99.254.114.190]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6d88125a191sm67790396d6.114.2024.12.04.08.13.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Dec 2024 08:13:08 -0800 (PST) Date: Wed, 4 Dec 2024 11:13:06 -0500 From: Peter Xu To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Muchun Song , Andrew Morton , Guillaume Morin Subject: Re: [PATCH v1] mm/hugetlb: don't map folios writable without VM_WRITE when copying during fork() Message-ID: References: <20241204153100.1967364-1-david@redhat.com> MIME-Version: 1.0 In-Reply-To: <20241204153100.1967364-1-david@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: KJpzjwPutaxRO2hXw26Vxx3rhqaczcmiLizB9zckQ60_1733328790 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: B998F40009 X-Stat-Signature: xh18u9zyj1m4rnyxz4m3omn6xm36q63z X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1733328785-140328 X-HE-Meta: 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 mxLZpArd 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, 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, Dec 04, 2024 at 04:31:00PM +0100, David Hildenbrand wrote: > If we have to trigger a hugetlb folio copy during fork() because the anon > folio might be pinned, we currently unconditionally create a writable > PTE. > > However, the VMA might not have write permissions (VM_WRITE) at that > point. > > Fix it by checking the VMA for VM_WRITE. Make the code less error prone > by moving checking for VM_WRITE into make_huge_pte(), and letting > callers only specify whether we should try making it writable. > > A simple reproducer that longter-pins the folios using liburing to then > mprotect(PROT_READ) the folios befor fork() [1] results in: > > Before: > [FAIL] access should not have worked > > After: > [PASS] access did not work as expected > > [1] https://gitlab.com/davidhildenbrand/scratchspace/-/raw/main/reproducers/hugetlb-mkwrite-fork.c > > This is rather a corner case, so stable might not be warranted. > > Fixes: 4eae4efa2c29 ("hugetlb: do early cow when page pinned on src mm") > Cc: Muchun Song > Cc: Andrew Morton > Cc: Peter Xu > Cc: Guillaume Morin > Signed-off-by: David Hildenbrand Acked-by: Peter Xu Thanks, -- Peter Xu