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Received: from 30.74.144.153(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XCoZJ.D_1791967088 cluster:ay36) by smtp.aliyun-inc.com; Wed, 14 Oct 2026 16:38:09 +0800 Message-ID: Date: Wed, 14 Oct 2026 16:38:08 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64/mm: restrict transparent contpte mappings to valid PTEs To: Lance Yang , Zhao Gongyi Cc: catalin.marinas@arm.com, will@kernel.org, ryan.roberts@arm.com, dev.jain@arm.com, mark.rutland@arm.com, akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20261013093600.54995-1-zhaogongyi@bytedance.com> <20261013153953.77575-1-lance.yang@linux.dev> <516828fb-558d-4a20-9532-51f50d6ba042@bytedance.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 2411220008 X-Rspam-User: X-Stat-Signature: ybsgfgc8ifkisbd88kfiukx6gnocdz5r X-HE-Tag: 1791967092-324105 X-HE-Meta: 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 uqOMXPj7 i/3Es7iC8osXU79qf5KuSWZi8ZW/Ujegntz1axgosSOKzwW5Hw8eeL/uoAm1fZlIeiuGmCuqX113ueWcltEElxvhlSxPRgm98I0ogIwx/OBNzI0x6LTZEuaMKD6/z8EzIu0XSiUKQDzgmH7gROKdBUv8+0KOEsFa57pt03JpjKlvwB5U9jGXr1Bs8TPTtYDuEL2Z2zOrqGhEyILpdt8koJkrlNNlHAIAFj8G+HJNFUXIQyTj1f3nUeOL3s8yqbgTfFZDQYeInwRoRyivkpDYtGnMi6JXv1KpwKz8jl1/XXO6qNjQ92287ZIfbRcHnJ+Sxrw9nfbIsYbpt8k4mupx2plYVKw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/14/26 2:46 PM, Lance Yang wrote: > > > On 2026/10/14 14:31, Zhao Gongyi wrote: >> On 10/13/26 11:39 PM, Lance Yang wrote: >>>> >>>> +    /* >>>> +     * Keep the producer-side invariant documented in pgtable.h >>>> true even >>>> +     * if a direct caller passes an invalid descriptor with >>>> PTE_CONT set. >>>> +     */ >>>> +    if (!pte_valid(pte)) >>>> +        return __set_ptes(mm, addr, ptep, pte_mknoncont(pte), nr); >>> >>> set_ptes() is the only in-tree caller, and it already clears PTE_CONT >>> before we get here ... no? Why not fold !pte_valid(pte) into the >>> !mm_is_user(mm) check below and return __set_ptes() directly? >>> >>>     if (!mm_is_user(mm) || !pte_valid(pte)) >>>         return __set_ptes(mm, addr, ptep, pte, nr); >>> >>> If a direct caller does pass a !pte_valid PTE with PTE_CONT set, I'd >>> rather add a VM_WARN_ON() to catch that. Silently clearing the bit would >>> hide a caller bug :) >>> >> >> Hi Lance, >> >> Thanks for taking a look. > > Cheers! > >> Yes, you are right. The public set_ptes() wrapper already strips PTE_CONT >> before calling contpte_set_ptes(), so the pte_mknoncont() in the invalid >> path is unnecessary for the current in-tree path. >> >> The issue I was trying to avoid is not that the incoming pte already has >> PTE_CONT set, but that contpte_set_ptes() rebuilds the pte from pfn/prot >> and then adds PTE_CONT again based on alignment. For an invalid >> descriptor, >> that transparent contiguous encoding should be skipped entirely. >> >> So your suggested shape makes sense to me. I will change this to return >> through __set_ptes() directly for invalid descriptors, and add a warning >> for any unexpected direct caller that passes an invalid PTE with PTE_CONT >> set, e.g.: >> >>     if (!mm_is_user(mm) || !pte_valid(pte)) { >>         VM_WARN_ON_ONCE(!pte_valid(pte) && pte_cont(pte)); mprotect() can trigger the warning here when setting PAGE_NONE for a batch of PTEs? >>         return __set_ptes(mm, addr, ptep, pte, nr); I am trying to convince myself that the 'nr' passed in is always CONT_PTE_SIZE aligned, but it seems OK.