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 BA78CCC6B1F for ; Wed, 14 Oct 2026 09:24:41 +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=rVBZSWzhmTgsQbjaqm+RNdeGA3BriAh5gCRFbByzJ/o=; b=DxWMXJI6bMJiH0cAliWoOIVJ/P +wzvVwE7TSCBU/h8e0SbKsft6drwuSPNSwGjAUek/L1yeShcWU4mJRVsqvLxZtRsc2NwgMHDBMu8+ EidL8U+FH94pvwbxYoY+0LFuNBoqV/YnT41fSd1h+lEuA64k1guwq2lPhy6ZOGcwqn9ob6P+Vdf+Y /lLsCSL8XpU3TKP8Ko9i6cNwnRENZ29JALCz4MH8V2J7AqPmtF+pmDEtY1REhMUCytVyA781gBbMt jPlMXGxohczyiZkGtz3wBcyIe12iPH6xcElwQ+f44jW2zK6QmsLoyICfztaC29eW/PjkbLjBDIHL7 06x4tpjg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xGvDs-0000000F1Qz-0cHz; Wed, 14 Oct 2026 09:24:32 +0000 Received: from out-114.mta1.migadu.com ([2001:41d0:203:375::72] helo=mta1.migadu.com) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xGvDo-0000000F1Pj-0U5u for linux-arm-kernel@lists.infradead.org; Wed, 14 Oct 2026 09:24:30 +0000 X-Envelope-To: linux-arm-kernel@lists.infradead.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=1791969866; v=1; x=1792574666; b=QsAt5ZEclRMMg12FhNOY82qAWJ43LLKUyGzqS4fUrOpY2hevdQaeubEMXxB/gT+X9a/DMywM ImjsyePcYO+M+dJNxL4/8ba7gQIOVXkPxbO15BPSuiMJ4vDSUkx8SSKT5S7XHUuMmGnLe/V8kZJ eydlowQxz6sJpXiH1mKOqIkY= X-Envelope-To: linux-arm-kernel@lists.infradead.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 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261014_022428_303869_C176CD81 X-CRM114-Status: GOOD ( 14.60 ) 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 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