From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-98.mta1.migadu.com [95.215.58.98]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5FC923E1CED for ; Wed, 14 Oct 2026 09:24:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.98 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791969870; cv=none; b=dO++1vwEghvB7iKcDVU5iHQPq+jP/eNK4qy4SZWz4R0nb/5GF9xhjVjNTbATlHPN6bTHdImvnPOVLEkODnbX4LiB1BVN7Mr80cHk4CvwqsOtgcpD1TtywJZN4akKE7IVSECElJhlI6CN0BvGPC6z1hOBnhoS8AW9AbqLwB213F8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791969870; c=relaxed/simple; bh=9Rp6gok1+Kio/TSq1E9OFvpUWzUtlcEW1k6DFeMPFSc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=r4Ah/r93MWUaylQeCFQ1SchbJ5nnvPLj0kxlKmd2WnLGUCJF2tmXq8Z5CzU3JuLIHhDoFd/v9+MQi9y0q7UwQczMMDliRDnhq7/w/qV9gt8XLDEeIFAXku/TGlK5Bi3ztXmQeEMYDag+ehN7lDuRRLWeN1fCfzOr4xtW+swTH+Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=JAVBCnpl; arc=none smtp.client-ip=95.215.58.98 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="JAVBCnpl" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=9Rp6gok1+Kio/TSq1E9OFvpUWzUtlcEW1k6DFeMPFSc=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1791969865; v=1; x=1792574665; b=JAVBCnplvCbeKZl/JMDYbx2XfdKASjfrgzyZcBQgCeAwhRclpCVnMlD5EI5AfTK0D+TU4Ege oPnzfO5/QqZcOrOhaDCXAsNCAKisNa83gtXcpc4jdRIyhZKN8RLpQ0JY+mXMRxtBeNbd4q5bvJa MoCNL1khmzGusLotplHPv1RE= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id f4836833ee7be581; Wed, 14 Oct 2026 09:24:25 +0000 X-Mizu-Trace-ID: f4836833ee7be581 X-Migadu-Flow: FLOW_OUT Message-ID: Date: Wed, 14 Oct 2026 17:24:15 +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: Baolin Wang , 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> Content-Language: en-US From: Lance Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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 :) >>>         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. Cheers, Lance