From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-82.mta1.migadu.com [95.215.58.82]) (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 9911B47F787 for ; Wed, 14 Oct 2026 06:46:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.82 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791960402; cv=none; b=sFWVA2bNjGFjlo8Pa0V8+PfWdyQLXFuFBO0sSKRXIq4spUhKbUL2xVs82vQCTyWHrx0f/SZpVWQ01BaIqYrTHDC6hqFGr1bBHrKf3EvTYP3TU7rK2C9jKtjOzmGH3J2/hflx6k+taPN/C0UOvt3pqoTsbGGBQI5IDborVGMpC1Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791960402; c=relaxed/simple; bh=JLmTAoue8gGf1ERWgAb5UXzBAVBda1/ywkl4q8ms6rw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IHC0A4RD0jC3WQDGobjuMT/Lb/piZNVZjnH/GNPUanGDg/2Rxx2zU1SBfyvyIBPkbhYf/+/mOfiG//xNOeKTm8mhEMFBDiQo1TpPNC8+ZuT4RZfYvDj8Ng14RPUJaPbOObv1cGHIC20l/aotC86p4XauTUujsCzT48i03TF2UWU= 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=XduXr+NW; arc=none smtp.client-ip=95.215.58.82 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="XduXr+NW" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=JLmTAoue8gGf1ERWgAb5UXzBAVBda1/ywkl4q8ms6rw=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1791960394; v=1; x=1792565194; b=XduXr+NWEQc2k1ced2e4wi+9s8WN76WAicldStKItAcufoJI3wVXZKFuaTRVUBF7ND96HqvN R0eN5dIVH8BZYV8hJprCPN82Jcgo77XC6FmBjysbkspL0JlH5jDAJN1pNq1vsLzkIQt/NFOchYo W3JiTblzWUaZR9iCpLyqRV+0= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id b9d4fb5be1186799; Wed, 14 Oct 2026 06:46:34 +0000 X-Mizu-Trace-ID: b9d4fb5be1186799 X-Migadu-Flow: FLOW_OUT Message-ID: Date: Wed, 14 Oct 2026 14:46:21 +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 Content-Language: en-US To: Zhao Gongyi Cc: catalin.marinas@arm.com, will@kernel.org, ryan.roberts@arm.com, dev.jain@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> From: Lance Yang In-Reply-To: <516828fb-558d-4a20-9532-51f50d6ba042@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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)); > 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 for the quick fix! Nothing jumped out at me :) With that: Tested-by: Lance Yang