From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 63A391B4248; Mon, 19 May 2025 09:08:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747645727; cv=none; b=AODgUnZKAdxa8LQQFDYq7uScqeJrSws1T+WzyNa0pIkCioubh9E1Yri/AjrgjBTTF03M5yzcvGNhGhY66KOlyaseMnCvCTTuJ4m73uIK0L+cT2fqYzSusS9TGrF0f+OozSGtmcIgpAW0JvG97NNwlNho0ZRexQSqdLZz+8QOyh4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747645727; c=relaxed/simple; bh=qDvYY1v4Y0BU963Hawd5E4mFGQJhIeIKAwmTeH1m+F0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=AEYC+n5iBhZDMNOV/lCHy+JnSEfM1b2IIfhjXk7YmOv1vMvinpt90ppKVfjwf6g/ytoe5Ai5ByMs9kfhlPIRRSGGFVd43nShAtQ+UMKgeTs1GR7wqZagMQT9LE7TElisEjT4jLpmd9P56TupQCKLW79airE8dGaMX9KG0k2PnTM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 543B51655; Mon, 19 May 2025 02:08:28 -0700 (PDT) Received: from [10.57.95.69] (unknown [10.57.95.69]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BEE2E3F6A8; Mon, 19 May 2025 02:08:39 -0700 (PDT) Message-ID: <5763d921-f8a8-4ca6-b5b5-ad96eb5cda11@arm.com> Date: Mon, 19 May 2025 10:08:38 +0100 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 v2] arm64: Restrict pagetable teardown to avoid false warning Content-Language: en-GB To: Dev Jain , catalin.marinas@arm.com, will@kernel.org Cc: david@redhat.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: <20250518095445.31044-1-dev.jain@arm.com> From: Ryan Roberts In-Reply-To: <20250518095445.31044-1-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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. But the arm64 arch code always uses READ_ONCE() for dereferencing pgtable entries for safely. Perhaps we should be consistent here? if (pmd_present(READ_ONCE(*pmdp))) > + pmd_free_pte_page(pmdp, next); > } while (pmdp++, next += PMD_SIZE, next != end); > > pud_clear(pudp);