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 D16DCC3ABDD for ; Tue, 20 May 2025 09:07:35 +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: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=q6hN8clUXqHF54vif6K3GnNrSQmWL82ab7vlFINAuAw=; b=uSMbqX/3ieBJdm80X6xjebSqmk j0RZInBVXSTeAA0e4UFsux4L8N0rstfkBPN/JCfke100Uz2SoaNWd/d0hgH+EH/dTPEf+TuONAmu+ t2HIWRXuYycWtRUohnki9x0G36dn3aGSrnQnpq8jQPVSGk4XP+CkgCdzpP+debRO46iSGjms0HPN+ Nm97zjumS8e2gWaaaPr1IJQq8Hi+9m+GIHMt/uw3Bu3nkAhvLFUVbEOf+bu82GfRCv+Fi3PRX76oo xadon3aPVm2KqVRkvClGj5YRzHcik4YV4BVLD+k5IcT+nC4VOXYhIYQOVmRWP0lURpDjCiX6l3Xe7 S3qkNG6A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uHIwZ-0000000C8M9-2g1t; Tue, 20 May 2025 09:07:27 +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 1uHIuR-0000000C896-40Ou for linux-arm-kernel@lists.infradead.org; Tue, 20 May 2025 09:05:17 +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 602C3153B; Tue, 20 May 2025 02:04:59 -0700 (PDT) Received: from MacBook-Pro.blr.arm.com (unknown [10.164.18.48]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 365303F5A1; Tue, 20 May 2025 02:05:08 -0700 (PDT) From: Dev Jain To: ryan.roberts@arm.com Cc: anshuman.khandual@arm.com, catalin.marinas@arm.com, david@redhat.com, dev.jain@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, mark.rutland@arm.com, stable@vger.kernel.org, will@kernel.org, yang@os.amperecomputing.com Subject: Re: [PATCH v2] arm64: Restrict pagetable teardown to avoid false warning Date: Tue, 20 May 2025 14:35:01 +0530 Message-Id: <20250520090501.27273-1-dev.jain@arm.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250520_020516_037685_D0BACE17 X-CRM114-Status: GOOD ( 18.97 ) 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 19/05/2025 13:16, David Hildenbrand wrote: > On 19.05.25 11:08, Ryan Roberts wrote: >> On 18/05/2025 10:54, Dev Jain wrote: >>> Commit 9c006972c3fe removes the pxd_present() checks because the caller >> >> nit: please use the standard format for describing commits: Commit 9c006972c3fe >> ("arm64: mmu: drop pXd_present() checks from pXd_free_pYd_table()") >> >>> 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. Thus it is possible to >>> hit a warning in the latter, since pmd_none => !pmd_table(). Thus, add >>> a pmd_present() check in pud_free_pmd_page(). >>> >>> This problem was found by code inspection. >>> >>> This patch is based on 6.15-rc6. >> >> nit: please remove this to below the "---", its not part of the commit log. >> >>> >>> Fixes: 9c006972c3fe (arm64: mmu: drop pXd_present() checks from >>> pXd_free_pYd_table()) >>> >> >> nit: remove empty line; the tags should all be in a single block with no empty >> lines. >> >>> Cc: >>> Reported-by: Ryan Roberts >>> Signed-off-by: Dev Jain >>> --- >>> v1->v2: >>> - Enforce check in caller >>> >>> arch/arm64/mm/mmu.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >>> index ea6695d53fb9..5b1f4cd238ca 100644 >>> --- a/arch/arm64/mm/mmu.c >>> +++ b/arch/arm64/mm/mmu.c >>> @@ -1286,7 +1286,8 @@ int pud_free_pmd_page(pud_t *pudp, unsigned long addr) >>> next = addr; >>> end = addr + PUD_SIZE; >>> do { >>> - pmd_free_pte_page(pmdp, next); >>> + if (pmd_present(*pmdp)) >> >> pmd_free_pte_page() is using READ_ONCE() to access the *pmdp to ensure it can't >> be torn. I suspect we don't technically need that in these functions because >> there can be no race with a writer. > > Yeah, if there is no proper locking in place the function would already > seriously mess up (double freeing etc). Indeed; there is no locking, but this portion of the vmalloc VA space has been allocated to us exclusively, so we know there can be no one else racing. > >> But the arm64 arch code always uses >> READ_ONCE() for dereferencing pgtable entries for safely. Perhaps we should be >> consistent here? > > mm/vmalloc.c: if (pmd_present(*pmd) && !pmd_free_pte_page(pmd, addr)) Yes, I saw that. I know that we don't technically need READ_ONCE(). I'm just proposng that for arm64 code we should be consistent with what it already does. See Commit 20a004e7b017 ("arm64: mm: Use READ_ONCE/WRITE_ONCE when accessing page tables") So I'll just use pmdp_get()? (Hopefully my reply comes fine, I am replying from the terminal) Thanks, Ryan > > > :) > > Acked-by: David Hildenbrand >