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[2003:cb:c73b:fa00:8909:2d07:8909:6a5a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-440a5394bfasm151677125e9.40.2025.04.29.02.27.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 29 Apr 2025 02:27:45 -0700 (PDT) Message-ID: <9a770aec-a020-4199-a53e-eddda657999d@redhat.com> Date: Tue, 29 Apr 2025 11:27:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 6/7] mm: Batch around can_change_pte_writable() From: David Hildenbrand To: Dev Jain , akpm@linux-foundation.org Cc: ryan.roberts@arm.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, vbabka@suse.cz, jannh@google.com, anshuman.khandual@arm.com, peterx@redhat.com, joey.gouly@arm.com, ioworker0@gmail.com, baohua@kernel.org, kevin.brodsky@arm.com, quic_zhenhuah@quicinc.com, christophe.leroy@csgroup.eu, yangyicong@hisilicon.com, linux-arm-kernel@lists.infradead.org, namit@vmware.com, hughd@google.com, yang@os.amperecomputing.com, ziy@nvidia.com References: <20250429052336.18912-1-dev.jain@arm.com> <20250429052336.18912-7-dev.jain@arm.com> <25dcf969-e479-4d4a-a95c-0e83706af99e@redhat.com> Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 0E3771C0003 X-Stat-Signature: a9u8uf4p8bja6y3b355bbeeopfmi5wzs X-Rspam-User: X-HE-Tag: 1745918869-138604 X-HE-Meta: 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 45THF5as KXrbtHEY2wgXu97uvePov1rWNDDisoROPNT7DogpsLZ8M3Ar2OzeoiTAHgRu/9eb+cTzM3DmmjnbBXLvoc4Pa08jxwS3GcHk7Lw3weCiDhibfUJwy40GckffCoLgH//XFly2fj6oyUerEFCtaqtXC2bXbciH7n4J2dkTjlMLDCNpMwTC9ZV7XPWbsrm6yCnBBJwe9ymJr0fLtAvFogGxb2vUKyHlSagrdMUFqvcR5yNFwQKpSMzUINW+Q6iu6C8W7+lWE5t/drcMDAstopL4elIJtjnU8LWebHi3u6HXOwNUYt5E393K6pU99x+8LG3McjVvl/XRgsSkfixC1/soSGxu6ECaUutsRK6ovw+PTnEU3xn9XUzXMAoAQTYKgcqIG+c0e3tjSXSM6+ZsW+cVigKxtLoM92zt89jEJGWouUHZMRSIxxK14i6feoOd+5ORlAjFxXsrQYzmknY8= 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 29.04.25 11:19, David Hildenbrand wrote: > >> #include "internal.h" >> >> -bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr, >> - pte_t pte) >> +bool can_change_ptes_writable(struct vm_area_struct *vma, unsigned long addr, >> + pte_t pte, struct folio *folio, unsigned int nr) >> { >> struct page *page; >> >> @@ -67,8 +67,9 @@ bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr, >> * write-fault handler similarly would map them writable without >> * any additional checks while holding the PT lock. >> */ >> - page = vm_normal_page(vma, addr, pte); >> - return page && PageAnon(page) && PageAnonExclusive(page); >> + if (!folio) >> + folio = vm_normal_folio(vma, addr, pte); >> + return folio_test_anon(folio) && !folio_maybe_mapped_shared(folio); > > Oh no, now I spot it. That is horribly wrong. > > Please understand first what you are doing. Also, would expect that the cow.c selftest would catch that: "vmsplice() + unmap in child with mprotect() optimization" After fork() we have a R/O PTE in the parent. Our child then uses vmsplice() and unmaps the R/O PTE, meaning it is only left mapped by the parent. ret = mprotect(mem, size, PROT_READ); ret |= mprotect(mem, size, PROT_READ|PROT_WRITE); should turn the PTE writable, although it shouldn't. If that test case does not detect the issue you're introducing, we should look into adding a test case that detects it. -- Cheers, David / dhildenb