From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3EC761D47AC; Thu, 25 Jun 2026 07:56:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782374214; cv=none; b=XADpyWgAtEFP3J1/FBBtbKTyYhOCT30fOQUL8AsFE8eXVsW3Ijf8T5gLF2bADngva/hZIOpsoA1YMehw5Y6J0M0YAtNwaW1rOHu5a3UrUtObMnKQFkKnqcLo1ZJbUqTxUvZyS2l12cScxmYNC7ptOrIyDXn8oScme8tMrNJjm2s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782374214; c=relaxed/simple; bh=f3CgPYvjqOChOn+obzej8vXe6MGJn5QL9utAatZR9zA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=u9rG4J6x+dlxLCcGmxprzUHvuJRJWFgVVDhsUelEKrIW2MkVmz5nEEcDgAHC39u37NnM4TgjRLFndZ4ypBUeZxE5bw5Bq8LtAPoy8X/eQo6Ab+wiQ2GKkMaZ+7wCipytBSl1fyW3iE8dCaFxkWk8zlde4s5QhFT3Nkime6ZLKKg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Sx5k9p5v; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Sx5k9p5v" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 33AA01F000E9; Thu, 25 Jun 2026 07:56:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782374212; bh=OkLdmWeXxP7Oi0BCM7+2L8XOA1JIZ57KBqhE89bZ8/s=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Sx5k9p5v665BEWYXTxcVC05749Bo32HMTyJnP22MWIscfGJRosgdU4N4F3+X2x0Af ouRSAUStQ1CzNOywznEuK8Iwoe/YO8uA08/oE2kxQEIFDO8cXz3L/Z4pqABaQqk97m 0OkcRXML+4r5jCn31IloBPUwpKgaMfRv3D/Etz+yF+CIe8VKXQzQc407nRE6ETSIR5 1B+OMnpIEkfKlm1267ul9r9YUnU+yBTrokB6ECiwSKPqecAXYLZKZsHgqMtAj2GvIE PZBm3l7NoGsfpclQ57vspDvPMY+CYXe2O7zsDrfOPO4j9a6Z4sHGWIfRi2geCmKoYU V0NrO+POW9FCw== Message-ID: Date: Thu, 25 Jun 2026 09:56:47 +0200 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] mm/rmap: use huge_ptep_get() in try_to_unmap_one() To: Dev Jain , akpm@linux-foundation.org, ljs@kernel.org Cc: riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, kas@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, stable@vger.kernel.org References: <20260625042853.2752898-1-dev.jain@arm.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 On 6/25/26 06:28, Dev Jain wrote: > try_to_unmap_one() handles hugetlb folios when memory failure needs > to replace a poisoned hugetlb mapping with a hwpoison entry. In that > case page_vma_mapped_walk() returns the hugetlb entry in pvmw.pte, but > the code reads it with ptep_get() before decoding the PFN. > > That is wrong on architectures where hugetlb entries are not encoded as > regular PTEs. On s390, for example, a raw huge RSTE must be converted > by huge_ptep_get() before helpers such as pte_pfn() can inspect it. A > raw decode can select the wrong subpage, so try_to_unmap_one() can > install a hwpoison entry for the wrong PFN. > > The userspace-visible result is that a later access to the poisoned > hugetlb subpage can miss the expected SIGBUS. With DEBUG_VM, the wrong > subpage can also trip the PageHWPoison check. > > Use huge_ptep_get() for hugetlb mappings before decoding the PFN. > > Before c7ab0d2fdc84, the bug existed in the form of a plain dereference: > we would check the head page pfn of the hugetlb with pte_pfn(*pte), and > bail out on mismatch. This would mean that the hwpoisoned entry will not > get installed. > > I am not sure what is the procedure on such kinds of very old bugs - how > back should I really go? > > Fixes: c7ab0d2fdc84 ("mm: convert try_to_unmap_one() to use page_vma_mapped_walk()") > Cc: stable@vger.kernel.org > Signed-off-by: Dev Jain > --- > Applies on mm-unstable (d17fe8a046a2). > There are similar old bugs present, in try_to_migrate_one(), check_pte(), > remove_migration_pte(), prot_none_hugetlb_entry(). Yeah, we should handle all these cases properly. Can you send fixes? Using ptep_get() on something that's not a PTE entry is shaky on some architectures. -- Cheers, David