From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4FB5439FCC8; Wed, 14 Oct 2026 09:35:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.113 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791970519; cv=none; b=Cc5QW0CSNLNzcjKeb3dhtedBlcZRJ/nBPZu7sp/K6mSkrcHNQ+BKR176uHeXIsgWLY0A1u+ML0e2HKzLepssv4zbLpim3OQHUFzSG+CNh1ZMP44CdHylhlzCvKw7N9X2dhCS9+PER6/vStm3c07A2+1TiMRLJw7PMFXB5cfSpUM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791970519; c=relaxed/simple; bh=rhv7Pu9rDMzNcdT1lOeqV5Zm1Fcwd3i6HmYHbwAY7G4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tq/DO5UN8P/FZBph71+18R8YowypTTLpdu+7WDnsOdI/81VuWDcu7ljhETlrueD9Cs2h8m+WOj9PJe/wSKPPki9oSPBfVVWiWTL8qn+h4Aj9dYXa2Mxu45LbLmMF1Epo4O+Dw+oNvh6WMErPf+emT6WZSdIGzWU3yIOgb0zuHug= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=v4NEd6wT; arc=none smtp.client-ip=115.124.30.113 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="v4NEd6wT" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1791970512; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=lzQV53UhB9WLFXZ3kw7JuyZ+RL9WPK13e0F8BsUv4g8=; b=v4NEd6wTddCtpssZRpdb4Id5BURoD7vWQxFh+Y1J4PQLkq+QhZftk/BOJGuvkPQL9D+K2FNB763Whyo0DKF73CrujdXNnPqF/fXVOQmNmNVxYdwFdYE8KSDok78WWOBHHZCnBKh+2B0J8NUSR4Jq/8was7pAN/QpwhWYuX1Abrw= 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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