From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 927793D3319; Wed, 25 Feb 2026 15:23:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772033013; cv=none; b=mlIFjYLtIt1ErCKLPiZiXN4dhquFUbL2OlGU6blCDxbq8EtX7alBa5QfioaV4Lrd1kfSVHMoKgRayMpacavOwhZEdXOvqJVXPUWstC4ly7TEQg3phhVC5e4FplvFVqtbbfHthk5QVPAI8uCCR8XAq+xnx1raeLPf2joi2s6AjhQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772033013; c=relaxed/simple; bh=gS5Yk7wYTW6W1m8o50Cew7D6B1+VreaVyadftIITtbc=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=T1/e6Heb3MwRl2ZfnXd6h4wJu6bCXQo4vF61M73X0TqGv1tU5tirN+aBC2Ly4XkJVsH7tOmU3Fo9VX/IIIPf7OAx6Wgz9kq1ihoaro05wvCiMzHpOWPPM9NTDc72A2ITl2KSCUeAYSifFPgxREJIcpPIvKvAQJBmFdPKYO1NIqY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Dg1fRSCg; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Dg1fRSCg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 43831C116D0; Wed, 25 Feb 2026 15:23:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772033013; bh=gS5Yk7wYTW6W1m8o50Cew7D6B1+VreaVyadftIITtbc=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=Dg1fRSCg7k3Q2cK9Sat615Pj7Jh0PALjT32x9LczwQkRJEkfcOlRGlQvCq/OfhtyQ SU+aTqkoeOQMHGt6s/Oc6VC6xrwccygDUgzu9ii4MyuDMtNBqzDgwChPufMaqkCzgW uLHQuo0VgJ3QxnXTbIKkqcDWrcpBEy9VrmC46MD+elXPqK08UWyEego0mwNh+rYb/U S+LE3hsOmSqxwHWQdTfhsAZKOCUtomSxdHJr83Lo6JxATY49GUAn2ORLbpCLhZgnQh TkKAV3TTOwTwKGZmUrAHcmNEPdLEWUEV4ebP7hEtgoRnhX2bnpA2vQ14qhuC2nWPu2 EjcdY+vRMEt9w== Message-ID: <7da49940-e1a4-4018-9db1-208411598e77@kernel.org> Date: Wed, 25 Feb 2026 16:23:29 +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 1/2] mm/huge_memory: Fix use of NULL folio in move_pages_huge_pmd() From: "David Hildenbrand (Arm)" To: Chris Down , Andrew Morton Cc: Matthew Wilcox , kernel-team@fb.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <0b653dcd-842b-4360-bc1c-8fe779efbc23@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 2/18/26 08:52, David Hildenbrand (Arm) wrote: > On 2/18/26 04:45, Chris Down wrote: >> move_pages_huge_pmd() handles UFFDIO_MOVE for both normal THPs and huge >> zero pages. For the huge zero page path, src_folio is explicitly set to >> NULL (used as a sentinel to skip folio operations like lock and rmap). >> >> In the huge zero page branch, src_folio is NULL, so folio_mk_pmd(NULL, >> pgprot) passes NULL through folio_pfn() and page_to_pfn(). With >> SPARSEMEM_VMEMMAP this silently produces a bogus PFN, installing a PMD >> pointing to non-existent physical memory. On other memory models it >> is a NULL dereference. >> >> Use page_folio(src_page) to obtain the valid huge zero folio from the >> page, which was obtained from pmd_page() and remains valid throughout. >> >> Fixes: e3981db444a0 ("mm: add folio_mk_pmd()") >> Cc: stable@vger.kernel.org >> Signed-off-by: Chris Down >> --- >>   mm/huge_memory.c | 2 +- >>   1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 44ff8a648afd..fed57951a7cd 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -2794,7 +2794,7 @@ int move_pages_huge_pmd(struct mm_struct *mm, >> pmd_t *dst_pmd, pmd_t *src_pmd, pm >>           _dst_pmd = pmd_mkwrite(pmd_mkdirty(_dst_pmd), dst_vma); >>       } else { >>           src_pmdval = pmdp_huge_clear_flush(src_vma, src_addr, src_pmd); >> -        _dst_pmd = folio_mk_pmd(src_folio, dst_vma->vm_page_prot); >> +        _dst_pmd = folio_mk_pmd(page_folio(src_page), dst_vma- >> >vm_page_prot); >>       } >>       set_pmd_at(mm, dst_addr, dst_pmd, _dst_pmd); >>   > > God this code is horrible. > > Why can't we simply move the PMD like move_huge_pmd() would do and make > this code less error prone? > >     _dst_pmd = src_pmdval; > > According to validate_move_areas(), the permissions of both VMAs are equal. > > > We might have to handle it just like move_huge_pmd(): > >     _dst_pmd = move_soft_dirty_pmd(src_pmdval); > > To also set the softdirty bit. > > Then, we would want to just clear uffd. > >     _dst_pmd = move_soft_dirty_pmd(src_pmdval); >     _dst_pmd = clear_uffd_wp_pmd(_dst_pmd); > Chris, do you have time to follow up, or should I look into it? The issue looks quite bad, so we should tackle it ASAP. -- Cheers, David