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 7209C3CEB90; Thu, 2 Jul 2026 09:09:00 +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=1782983341; cv=none; b=tFQBJ1PmtefQ+dgaYi6emJu7aMQEq4duIhYDN39xOYYhCwFjADqAMRf28JLl3LXFrbY79OURIVvdrPAKTYvOzQsMAo+U/ZyovyqLI7MXn1RV4JGs2o1u9pgE4XfHVgrRYVGkp9ZWTAzofOGgLqWcse/sGsaAhcNC1ddCt2Rrlok= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782983341; c=relaxed/simple; bh=vCwix3VrRVa0qLybvbsy6PV5Ocf40WHZJfF5rvlVcUo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XpyeUYs+HqdQO+nBgvSrwTGHGLvlX6dwPnORyT82wiwbP10ZWHRU+F0GUhN5Yv2ttNMklrrYdPwWrSsRxVHnvZGGQ8jdpMyyL8PtNTgAg3Ud+e3iLPSWm1+sREw2W1zsgM0yl5Rbo0w1zSsIh0E6eSYb2oUwk1iMwepkArNu+tQ= 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=Z/uB3Ryt; 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="Z/uB3Ryt" 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 7BE54288E; Thu, 2 Jul 2026 02:08:55 -0700 (PDT) Received: from [10.164.19.15] (unknown [10.164.19.15]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F3A123F85F; Thu, 2 Jul 2026 02:08:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1782983339; bh=vCwix3VrRVa0qLybvbsy6PV5Ocf40WHZJfF5rvlVcUo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Z/uB3RytqoD94KC3C+8KsT7tF0rPMJKcCWTT/SCVOZRWqODg6FkDRSjxfpEYjUzot Cylok/Y1uVEHB0aip7ANYaNvgAbx/CyAMt6Xy8pjRnj1P7Kq5dX822Ql7kmM0d0RVm 3jetQLb9C+gPogZ7ztn5jJMo89lnnC0g+H9e07Dk= Message-ID: Date: Thu, 2 Jul 2026 14:38:48 +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 v2 2/6] 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, nao.horiguchi@gmail.com, ak@linux.intel.com, mel@csn.ul.ie, pfalcato@suse.de, jpoimboe@kernel.org, dave.hansen@intel.com, tglx@kernel.org, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.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: <20260702051341.126509-1-dev.jain@arm.com> <20260702051341.126509-3-dev.jain@arm.com> <97a43d82-28c2-4f98-ad74-fe05ed9f0297@linux.dev> Content-Language: en-US From: Dev Jain In-Reply-To: <97a43d82-28c2-4f98-ad74-fe05ed9f0297@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 02/07/26 2:17 pm, Muchun Song wrote: > > > On 2026/7/2 13:13, 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 >> Reported-by: David Hildenbrand >> 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); >> + > > Maybe I didn't express my thoughts clearly in the first version, let me > explain in more detail. > > We should define this stub as a no-op for !CONFIG_HUGETLB_PAGE (like > set_huge_pte_at, that is why I mentioned 5d4af6195c87c6 for your reference > in your previous version). Currently, you've added a declaration, but the > function itself doesn't actually exist, which seems quite strange to me. https://lore.kernel.org/all/a4fe8ba6-2ecd-4bb9-95a9-27f9f1e87d2e@kernel.org/ David suggested this. Honestly I quite like David's suggestion, what do you think? > > Muchun, > Thanks. >>   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); >>   >