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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ZzZ3EuQ2qjlvO7W7V1MYgf1owieL7IFjWffRoEL3LS4XoiUrOOsBiva2N3xoTaB3m ktyfzIBiW8F5zFoFUKnSoDcMAPPosaXEIG0VceWlD1JAPEHVIGBTHR8uURhM7gloEu EMDBhP4TLCF+Xc0McZABfw9o0Mr/DTa6Ivxb4efE= Message-ID: <0bbbe312-47a4-4eeb-8299-1f20daf4e949@arm.com> Date: Wed, 14 Oct 2026 15:33:34 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64/mm: restrict transparent contpte mappings to valid PTEs To: Zhao Gongyi , Lance Yang 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> Content-Language: en-US From: Dev Jain In-Reply-To: <516828fb-558d-4a20-9532-51f50d6ba042@bytedance.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: ppzuewh7m7ejbmihs5tcn8r3au9935xo X-Rspam-User: X-Rspamd-Queue-Id: 0326E40005 X-Rspamd-Server: rspam08 X-HE-Tag: 1791972222-953362 X-HE-Meta: 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 6aYoo5PO 5UI4IbRVVO1Jvt2mGjL960xqorZo57lhTlHadMYUU2YVtla/rbLBQUzB2ZAGvUvb7Ew/p2o57d/4rVFfn+RiE7ybDocTV0Ti1AKiH0EKbLhIq0z3KgeNEOMTgN6+vYWhVid2Fa86SHIaofjYE6YF/CWqNh3CuCqGRq8p90lHzAV83E7pa1N26fqNnK2KmeSegeGeH8Cb03KUT5tazi3lv/T5M0+jn4UW8bVkgtUtFt1IQKus= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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? > 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