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 B5FC33A2572; Fri, 26 Jun 2026 04:04:05 +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=1782446648; cv=none; b=luQXKUkrY4d2Ber5X8vksAgR5oE50GBuqTn1Vi3+D5yyqChHIEpVA/cbtiuTmEPKcJ9Q3ZBLev+PuxHqpY9Ol1UK4wm8NgIin94JHNdBoeN2I8bdsIMCYdH199LNP2qUDYbW4UyUP4wfsi1CL9m35Kqip2sub2m65yrR1sJ7tTs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782446648; c=relaxed/simple; bh=qyp2lulHzizESS3VvJ7MUIf08zH9IfJSzEnsUhYQo1I=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=VjiSww8f4XNr2r39bqHBvWXRcavFrBN9fFGa+8+2G38ob1Kc+rMF2YiQcVWhms16F9xmPAx1Ond0B+fP7HHciW9hvouLtN7sdv/AuyaQ+gcLDjWGD79DQh3qAHzP+28JH+TtTcxVSE55crpVTIDk8VBTsEHTegsVZZkjh4FLzX4= 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; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=o+AR3peA; 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 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="o+AR3peA" 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 0F4E522F8; Thu, 25 Jun 2026 21:04:00 -0700 (PDT) Received: from [10.164.148.34] (MacBook-Pro.blr.arm.com [10.164.148.34]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5EEBB3F905; Thu, 25 Jun 2026 21:03:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1782446644; bh=qyp2lulHzizESS3VvJ7MUIf08zH9IfJSzEnsUhYQo1I=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=o+AR3peAt7q1C40S6W9MFppuxdb25CQLrAWrtR13P67RSWbzktHKG5lZr8q7a84lq wXTAJUGfJaxcfotOWBWHCI3yYbLBuaBROgfdM4EpzGrwrqycBu5myzKUrHNm74dPhl OdlvlXwuj66UdCC8fFH6txyGOC040Gj+OZQvifGI= Message-ID: <4619650f-28b5-4fb4-91be-50daa0b4d84b@arm.com> Date: Fri, 26 Jun 2026 09:33:45 +0530 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 1/5] mm/rmap: use huge_ptep_get() in try_to_unmap_one() To: Muchun Song Cc: riel@surriel.com, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, kas@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rcampbell@nvidia.com, apopple@nvidia.com, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, mel@csn.ul.ie, nao.horiguchi@gmail.com, ak@linux.intel.com, j-nomura@ce.jp.nec.com, pfalcato@suse.de, dave.hansen@intel.com, tglx@kernel.org, jpoimboe@kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, stable@vger.kernel.org, osalvador@suse.de, akpm@linux-foundation.org, ljs@kernel.org, david@kernel.org, liam@infradead.org References: <20260625112955.3254283-1-dev.jain@arm.com> <20260625112955.3254283-2-dev.jain@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 26/06/26 8:47 am, Muchun Song wrote: > > > On 2026/6/25 19:29, 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 pte pointer to the hugetlb folio >> in pvmw.pte, but the code reads it with ptep_get(). >> >> On arches which provide their own huge_ptep_get() to dereference a huge >> pte pointer, accessing via ptep_get() would cause pte_pfn(), pte_present() >> etc to misbehave. >> >> It is not clear whether this has a trivially visible effect to userspace. >> >> Just use huge_ptep_get() for dereferencing a huge pte pointer. >> >> Fixes: c7ab0d2fdc84 ("mm: convert try_to_unmap_one() to use page_vma_mapped_walk()") >> Cc: stable@vger.kernel.org >> Signed-off-by: Dev Jain >> --- >>   include/linux/hugetlb.h |  3 +++ >>   mm/rmap.c               | 16 ++++++++++------ >>   2 files changed, 13 insertions(+), 6 deletions(-) >> >> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h >> index 2abaf99321e90..fdb7bdf7645c5 100644 >> --- a/include/linux/hugetlb.h >> +++ b/include/linux/hugetlb.h >> @@ -1261,6 +1261,9 @@ static inline void hugetlb_count_sub(long l, struct mm_struct *mm) >>   { >>   } >>   +pte_t huge_ptep_get(struct mm_struct *mm, unsigned long addr, >> +            pte_t *ptep); > > Thanks so much for the fix! I'm curious, though: why do we > need to add a separate declaration for this function here? For !CONFIG_HUGETLB_PAGE, compiler complains that there is no huge_ptep_get. So this is to make compiler happy. > > Thanks, > Muchun > >> + >>   static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma, >>                         unsigned long addr, pte_t *ptep) >>   { >> diff --git a/mm/rmap.c b/mm/rmap.c >> index 1c77d5dc06e9f..aa8a254efaecc 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -2095,11 +2095,16 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, >>           /* Unexpected PMD-mapped THP? */ >>           VM_BUG_ON_FOLIO(!pvmw.pte, folio); >>   -        /* >> -         * Handle PFN swap PTEs, such as device-exclusive ones, that >> -         * actually map pages. >> -         */ >> -        pteval = ptep_get(pvmw.pte); >> +        address = pvmw.address; >> +        if (folio_test_hugetlb(folio)) { >> +            pteval = huge_ptep_get(mm, address, pvmw.pte); >> +        } else { >> +            /* >> +             * Handle PFN swap PTEs, such as device-exclusive ones, >> +             * that actually map pages. >> +             */ >> +            pteval = ptep_get(pvmw.pte); >> +        } >>           if (likely(pte_present(pteval))) { >>               pfn = pte_pfn(pteval); >>           } else { >> @@ -2110,7 +2115,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, >>           } >>             subpage = folio_page(folio, pfn - folio_pfn(folio)); >> -        address = pvmw.address; >>           anon_exclusive = folio_test_anon(folio) && >>                    PageAnonExclusive(subpage); >>   >