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Received: from out-100.mta1.migadu.com ([2001:41d0:203:375::64] helo=mta1.migadu.com) by desiato.infradead.org with esmtps (Exim 4.99.5 #2 (Red Hat Linux)) id 1xGwUK-0000000Ge8Y-2pvF for linux-arm-kernel@lists.infradead.org; Wed, 14 Oct 2026 10:45:38 +0000 X-Envelope-To: linux-arm-kernel@lists.infradead.org DKIM-Signature: a=rsa-sha256; bh=4j71whs7pU+NnCMQt6l/U/Btk6pFemJHjPQ5tC3+JVI=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1791974733; v=1; x=1792579533; b=FYzHg0XnYGEUQq4gQZ5cIbHAgUUe4PpGS1L3xemdo1QSXQzcIC76202IsBVcUhpf6mVVskX/ XK4ZbrCHKtKxf26lrd1wGSJh0rbd9KbjJDTAkElHSfV7oM+6YU8/nTeRR4QAv4kDQFKqJpC0wiE r0uD1vFxp4NgP+ne0cKlS/C8= X-Envelope-To: linux-arm-kernel@lists.infradead.org Received: by smtp.migadu.com with ESMTPS id 767be9f59756f718; Wed, 14 Oct 2026 10:45:21 +0000 X-Mizu-Trace-ID: 767be9f59756f718 X-Migadu-Flow: FLOW_OUT Message-ID: <44aba42f-0355-4643-826f-0c7abec4499c@linux.dev> Date: Wed, 14 Oct 2026 18:45:11 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64/mm: restrict transparent contpte mappings to valid PTEs To: Dev Jain , Zhao Gongyi Cc: catalin.marinas@arm.com, will@kernel.org, ryan.roberts@arm.com, baolin.wang@linux.alibaba.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> <0bbbe312-47a4-4eeb-8299-1f20daf4e949@arm.com> Content-Language: en-US From: Lance Yang In-Reply-To: <0bbbe312-47a4-4eeb-8299-1f20daf4e949@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261014_114537_137020_1CE453B4 X-CRM114-Status: GOOD ( 14.59 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2026/10/14 18:03, Dev Jain wrote: > > > On 14/10/26 12:01 pm, 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. >> >> 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)); > > set_ptes does pte_mknoncont(), so the warning will *never* fire I think? YES. Just a sanity check to catch a future direct caller passing a !pte_valid PTE with PTE_CONT set, rather than silently clearing the bit :) Cheers, Lance > >> return __set_ptes(mm, addr, ptep, pte, nr); >> } >> >> That keeps the fix focused on not creating new invalid contpte entries, >> while still catching a bad direct caller instead of silently sanitizing it. >> >> Thanks, >> Zhao >