From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id F240CCC6B1D for ; Wed, 14 Oct 2026 09:41:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=eknjK7272CVNf6tS/VepL4H992+z6bNQqkyA1iFz+tQ=; b=kj0SmWnPzio0xwbxdLzLO8LBYx IrzrohEcWfzVNxwc9zbQCq56463dqnDr8QOZ5sgo7RlgMbceFqrQLiskKSmi9wOPuCYybxoFY09BH MIulCz3cjpgx5YGpElXBdwewGIpfw3bjSIBdcj5Di0StiwpYDNMhVm//jGS1+0wlTPTpzXmmrABs2 ZdunMHM1v27C5mL4BM1zOXMkXfy4advjOgUGTaGiShfMRj9EiN6O+Yoqd+EwUBRyj36t1MRr1ihmW MNc4vB2phAUQt6N8W33sgiz7Vdcaj8WXjxnr1gisfxHPIhv6qjfOLeDvJNYklYjcywUYs9/oJuylK R5x/jm5A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xGvUZ-0000000F5Sy-10X6; Wed, 14 Oct 2026 09:41:47 +0000 Received: from tor.source.kernel.org ([172.105.4.254]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xGvUS-0000000F5RJ-1sb3 for linux-arm-kernel@lists.infradead.org; Wed, 14 Oct 2026 09:41:41 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id ACF26601F9; Wed, 14 Oct 2026 09:41:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 57F731F0089F; Wed, 14 Oct 2026 09:41:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791970899; bh=eknjK7272CVNf6tS/VepL4H992+z6bNQqkyA1iFz+tQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=T5d8KMHdYrwyQOI2inOJa8WADx/WcYcVUhf6HVnoAs+XC9nXjkZm2J+GXmVN4C+jc MgD2TefOp8QXb1QXs11PcxQ7lerPEtPipacMohaLtsKHaicZ816//O0j1J2BqrJ7u0 sxvKsEnURNR0O3v1wZBuIrFfB+QxxR5C10+SqUwVEIsjX9etaC53NgnlBkohUuSFhF hAjUjxgM0DPiESCpMHF/2ONQp5IEVQfNDcFpnLi6DrnnttnyW0blAnb/eLM2H5EXed YGCBBmRzuqZcs7uFBQLBFsEQkUTNGcAHsgGQEGqTpK5Td6GAtZ7CxI6orrb7JvXAoU 3apxqry9108sA== Message-ID: Date: Wed, 14 Oct 2026 11:41:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64/mm: restrict transparent contpte mappings to valid PTEs To: Zhao Gongyi , catalin.marinas@arm.com, will@kernel.org, Ryan Roberts Cc: ryan.roberts@arm.com, dev.jain@arm.com, baolin.wang@linux.alibaba.com, lance.yang@linux.dev, mark.rutland@arm.com, akpm@linux-foundation.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> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org CCing Ryan: https://lore.kernel.org/r/20261013093600.54995-1-zhaogongyi@bytedance.com On 10/13/26 11:36, Zhao Gongyi wrote: > The transparent contpte layer treats PTE_CONT as software state: when a > PTE has PTE_CONT set, the contpte helpers may align the operation to a > CONT_PTE_SIZE block and operate on the whole block. That invariant only > makes sense for valid mappings. Explicit users such as hugetlb manage > their contiguous encodings separately. > > contpte_set_ptes() currently sets PTE_CONT from alignment alone. Batched > set_ptes() users can therefore install present-invalid PTEs with > PTE_CONT set, for example mprotect(PROT_NONE), NUMA hinting through > modify_prot_commit_ptes(), fork() copying a PROT_NONE large folio, or a > PMD split installing PAGE_NONE PTEs. > > This is not a hardware programming problem: invalid descriptors are not > translated, so the hardware ignores descriptor bits such as PTE_CONT. It > is a software-state problem. Some arm64 fast paths intentionally test > pte_cont() directly instead of pte_valid_cont(), for example commit > 9970a9a27ffc ("arm64: mm: implement the architecture-specific > test_and_clear_young_ptes()"). Fixing the producer side preserves these > fast paths and covers all consumers. > > In the observed failure, mprotect(PROT_NONE) installed a full > CONT_PTE_SIZE range of present-invalid PTEs with PTE_CONT set. > MADV_GUARD_INSTALL then zapped one PTE. The nr == 1 clear_full_ptes() > path only unfolds pte_valid_cont() entries, so the neighbouring > present-invalid entries kept PTE_CONT while the target entry became a > guard marker. Hm, is there a good reason why we cannot just use the cont-pte bit for all *present* PTEs, even if HW would not be prepared to benefit (!pte_valid())? I guess we really only have to make sure to shatter properly, right? -- Cheers, David