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 CAA27C2D0CD for ; Thu, 15 May 2025 08:29:39 +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=HvWciJfaVsMWvx3Zdk//3quO7yVMEY+q9znYmRIhlXA=; b=Cjx2pDE/6rH9oI/5dyEra/9lJg Z371KeaWk8JT1YAio7RliOWgcMKR1R5gTliIQcv2yI9Xd0dDxf065sEnVbBByKu0wV3HHuDZWwfma xQDqVeVxNZDZe82vEHomulOcfRVshadrfsq6pc1hREjjCTKC1CTVBKIZjYXgqjbFp+GmikTblV3sY XmLXk35ukmItbBVihxD3jK7oDtVD4M72ZyM3Mc/XwHy13MtWdUUigbFKZ689Vwr+LvYtm46eIGrtw UWxmn9uPPfZquZJLPVxaK9mpeRbabqBQvnmG+/UmRDhu7XM/LMMjmaLOyh/TYNwjuH9zo+yQVenqP IdlgXu/g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uFTy8-0000000HXeG-0S7v; Thu, 15 May 2025 08:29:32 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uFTrl-0000000HVPp-2dwL for linux-arm-kernel@lists.infradead.org; Thu, 15 May 2025 08:22:58 +0000 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 B5D5C14BF; Thu, 15 May 2025 01:22:44 -0700 (PDT) Received: from [10.162.40.26] (K4MQJ0H1H2.blr.arm.com [10.162.40.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8CD1A3F673; Thu, 15 May 2025 01:22:53 -0700 (PDT) Message-ID: <4904d02f-6595-4230-a321-23327596e085@arm.com> Date: Thu, 15 May 2025 13:52:50 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64: Check pxd_leaf() instead of !pxd_table() while tearing down page tables To: David Hildenbrand , catalin.marinas@arm.com, will@kernel.org Cc: ryan.roberts@arm.com, anshuman.khandual@arm.com, mark.rutland@arm.com, yang@os.amperecomputing.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org References: <20250515063450.86629-1-dev.jain@arm.com> <332ecda7-14c4-4dc3-aeff-26801b74ca04@redhat.com> Content-Language: en-US From: Dev Jain In-Reply-To: <332ecda7-14c4-4dc3-aeff-26801b74ca04@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250515_012257_728091_2F300C52 X-CRM114-Status: GOOD ( 13.39 ) 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 15/05/25 1:43 pm, David Hildenbrand wrote: > On 15.05.25 08:34, Dev Jain wrote: >> Commit 9c006972c3fe removes the pxd_present() checks because the caller >> checks pxd_present(). But, in case of vmap_try_huge_pud(), the caller >> only >> checks pud_present(); pud_free_pmd_page() recurses on each pmd through >> pmd_free_pte_page(), wherein the pmd may be none. > The commit states: "The core code already has a check for pXd_none()", > so I assume that assumption was not true in all cases? > > Should that one problematic caller then check for pmd_none() instead? From what I could gather of Will's commit message, my interpretation is that the concerned callers are vmap_try_huge_pud and vmap_try_huge_pmd. These individually check for pxd_present(): if (pmd_present(*pmd) && !pmd_free_pte_page(pmd, addr)) return 0; The problem is that vmap_try_huge_pud will also iterate on pte entries. So if the pud is present, then pud_free_pmd_page -> pmd_free_pte_page may encounter a none pmd and trigger a WARN. > > If you were able to trigger this WARN, it's always a good idea to > include the splat in the commit. I wasn't able to, it is just an observation from code inspection. >