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 265FF19F13F; Wed, 18 Feb 2026 07:52:38 +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=1771401158; cv=none; b=rfaUBaxuXRUCKD7urVJfItcdMR4mI7W8Mi315foq1w1ELHlgJb3cmcc2UswQcd/AZtKB4kDGoGXglqtAM6AdtgyKPzUSit+mbxOObY51/PJ0yPRdq/xHw1hkz+LvmZSGxmL5kWboJeU66DMM7HtBcES7CvClsD+WnR/yzznj4V8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771401158; c=relaxed/simple; bh=xHxjG4bDz4pgMox2OsAsfkgSSmmHF2eogXtvvKL0pkM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=d8pVjV6KFEsBw9IG2uGj41sT5Unf5yI5yFni4auguWt9b4l8C4BzO9XLDIBOhlFzZ+AtX4lltHsvIHGHSixCH8cFWYT0IUFC8vVHDpSKFW2dJTKYB4IfROgx/gSF8zZ5iv7qv36eSXBnfn2HQOfRkERDD86Fuj0OeCP76nm6BEY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XBFwv/J0; 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="XBFwv/J0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 49BC7C19421; Wed, 18 Feb 2026 07:52:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771401157; bh=xHxjG4bDz4pgMox2OsAsfkgSSmmHF2eogXtvvKL0pkM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=XBFwv/J0DHxfil/5yD6SPFQuYpECUHR5ZkFwRRYUuYJigiix4wzFkNC0ctIpYoBzr +B033FA2rkhfJBYWqPcqOcPyi+uvOk3iTMIFgQwOScyB/0CPD3YFTxLJRUCUQ2fwiF lx1Z61wkbIIabzOlIbr6+HAJ3RdLhPJuOLL+Lzb7hxNEusLBuOETkfMOZgrRp8akR/ iiOUz7ij/AH7Lu4BDp0/PXkbshEP+BDDL0M+SFKHh+4BxJq9glypyjclCQasxxJDAk nW6P7XLVtdmDlnomvjPB9+HnqAAPIGYomS1z5G9i8fux+VWWPhtrgYO+ocIaj6qL/4 4F3uFGDQRXr8w== Message-ID: <0b653dcd-842b-4360-bc1c-8fe779efbc23@kernel.org> Date: Wed, 18 Feb 2026 08:52:33 +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() 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: From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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); -- Cheers, David