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b=TuckBnnV2gndx2Shl2mQgAas0H0K8EeXutDAuWQtam0V0TwEeIIgy917J/NFDbN7sycibBI2Lr0OoHTyA76GpeMq6NGw7aG7Yh/zN6Osk9AoPSIpNEvhBrWqQYfR7r235NVFxsqw3DUkZAXGmrnBqZT9wGoUJ8wH+6Xy1FkeZ54= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R111e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037009110;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=19;SR=0;TI=SMTPD_---0XCoahw9_1791970509; Received: from 30.74.144.153(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XCoahw9_1791970509 cluster:ay36) by smtp.aliyun-inc.com; Wed, 14 Oct 2026 17:35:10 +0800 Message-ID: Date: Wed, 14 Oct 2026 17:35:09 +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: rspam11 X-Rspamd-Queue-Id: 15BD220008 X-Rspam-User: X-Stat-Signature: 8yr76aju5jge54ituzszacriftmwe147 X-HE-Tag: 1791970514-995412 X-HE-Meta: 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 +BgO5Dta zo/Ra9vPHgeEfaLhV9uKsq3PVxFoXkbmUuVvM9H9sCYwRfD/rmghe0TmlQL6q8S6/szQRXFyy1x6+H00Skt5prXyRQcj2B55IgC0JtxxQdOnXs8WTNYVXRoM1uLTszD7eI0xeMt5u2f5esEZuDXAorh1PLslG+wqkAu88e0gnrzjdie6kwtM3pJnSkG2n2mG3/+B4emeM/Fpipy/768ugFJtWIx92BavkSsNfbzXEtKVxluL1EslGAqTKiZR+cFTTvFhYWBT/rEvBRB13FO8W6H9itP5onYSBsJKlbIWdqlrnW+fTjw06iQpZTlHBWFjGn3V9cE0k/xCyX2M= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/14/26 5:24 PM, Lance Yang wrote: > > > On 2026/10/14 16:38, Baolin Wang wrote: >> >> >> 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? > > Nope. set_ptes() clears PTE_CONT before calling contpte_set_ptes(). > PAGE_NONE makes !pte_valid(pte) true, but pte_cont(pte) is false, > so the warning won't fire :) Ah, right. >>>>         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. > > Still nope :) > > IIRC, any partially covered contpte block should already be unfolded > by the time we get here ... > > We're just installing PTEs without PTE_CONT into cleared entries, > so nr doesn't need to be aligned to CONT_PTES. OK. I see. Thanks for explanation. So looks good to me. Reviewed-by: Baolin Wang