From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id E8A3449EC46; Wed, 14 Oct 2026 10:03:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791972225; cv=none; b=JUKLw/IT6bUgSt27ae+l2etmXaaaZFdvP6l9kr2jUw6ILwY9Scc81i5cRQf0FO5fpns7iBNMqTztGmvCHEWy40ZZyZJHhPRgJZ71I/IYfOSK8tHeQ1XREbFr6EFf1mmaRkVDnXnPipeldWjQYMGWy3Fj+TEIfF4SnhJZm0rKvnU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791972225; c=relaxed/simple; bh=eb+1OnhCrwcLrcQXmju+ZI4BR5IYqvlaJ9YM0fXSEG0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lpxipW2JFeTbawZ6b9QkiwAOSuR3NIFrc+vAIwthmhF4oZCCOdTRWzK5cufJDiN98QlNKzKd5sHaz+LNUSqoMIAewpqEKNQnaPkUZ9pMnIbOaJqrEX0s8cchLieuyylsGk+g2ajZEDq7lzyGA6y+4b0Tr2Ds3zmyM1TFWK4TUs0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=ZzZ3EuQ2; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="ZzZ3EuQ2" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CE654153B; Wed, 14 Oct 2026 03:03:38 -0700 (PDT) Received: from [10.164.19.62] (unknown [10.164.19.62]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5CD293F673; Wed, 14 Oct 2026 03:03:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1791972222; bh=eb+1OnhCrwcLrcQXmju+ZI4BR5IYqvlaJ9YM0fXSEG0=; 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 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: 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 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