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 DD4D6407572; Thu, 26 Feb 2026 15:17:36 +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=1772119056; cv=none; b=RRJOOtGbpQgzMtJUaTi7EAM4T5ylfd2JPCLaiStFVKAd3WbB1KLE6y9+0rF/yHwLP73uY8BLI8aifcyrzRd7r97lZkMh3r2mtCWsbD8IXBraD9SGZBAzXlYOhdk8RsY4ugWjwx2jxzaB1SlQKwsNVXWq9lKRcuqBRpT9Uz5VdtY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772119056; c=relaxed/simple; bh=aLGd9kkNNgUcYFmtIiy7QnU197IGoyxW/VYrnzMnoP0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qm8NI+rNEnnSJ+86m/Vfmr2ee9rKyyVFsFsmMkYGS8O9FCrwF3MFluHX/d7sNCVQiJxK7hF+m5NQgKaARIplNZj+/tUI3Gv3HRFjjmOgy+yazaZvF5ihUVs+0ZHeDqTPuwTHxBVxD7mRgEglQ0zYjYMTDE5gWkBcVKswNaF/6gI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mvqsq0kU; 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="mvqsq0kU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A073DC116C6; Thu, 26 Feb 2026 15:17:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772119056; bh=aLGd9kkNNgUcYFmtIiy7QnU197IGoyxW/VYrnzMnoP0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=mvqsq0kUH13XZgmV8wElxnONJYeKXRqcfRRtYItlQjBVZKxpIE/dc+ITxNhd6S1p3 T2AjMG/TXthk8J2aulk2q2MatA2xW+lUiBrhq/dJfzPp0Tvh1M45a6xqx+nCoimZB8 Pa2p1cUOqejG1LVB6MWXxv7ibGazvHkWUonN7OkkMkvDkN7+rPQj7hKLdKOjCbSJgJ Qs3pYm9sEqtL0C1RQDAZtPzelk+G+G4c8UXhxne2nTIChYjR15eVMDKR1l7R9/JRD3 WkhmvwuAcYqgQkKVomgYxqh5obrOaPBcUtP6Y0HGiJQzdwcykcopRA2JFm+oEdE2Gg 4xNbTcjO4nhSQ== Message-ID: <6147cf80-9d02-4c5c-ab81-8cb9b00044f0@kernel.org> Date: Thu, 26 Feb 2026 16:17:31 +0100 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] mm/huge_memory: Prevent huge zeropage refcount corruption in PMD move 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 Content-Transfer-Encoding: 7bit On 2/26/26 15:16, Chris Down wrote: > After commit d82d09e48219 ("mm/huge_memory: mark PMD mappings of the > huge zero folio special"), moved huge zero PMDs must remain special so > vm_normal_page_pmd() continues to treat them as special mappings. > > move_pages_huge_pmd() currently reconstructs the destination PMD in the > huge zero page branch, which drops PMD state such as pmd_special() on > architectures with CONFIG_ARCH_HAS_PTE_SPECIAL. As a result, > vm_normal_page_pmd() can treat the moved huge zero PMD as a normal page > and corrupt its refcount. > > Instead of reconstructing the PMD from the folio, derive the destination > entry from src_pmdval after pmdp_huge_clear_flush(), then handle the PMD > metadata the same way move_huge_pmd() does for moved entries by marking > it soft-dirty and clearing uffd-wp. > > Fixes: d82d09e48219 ("mm/huge_memory: mark PMD mappings of the huge zero folio special") > Cc: stable@vger.kernel.org > Signed-off-by: Chris Down > --- > mm/huge_memory.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index fed57951a7cd..8166b5e871ad 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2794,7 +2794,8 @@ 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(page_folio(src_page), dst_vma->vm_page_prot); > + _dst_pmd = move_soft_dirty_pmd(src_pmdval); > + _dst_pmd = clear_uffd_wp_pmd(_dst_pmd); Please squash that patch directly in #1. It doesn't make sense to leave something partially fixed in #1. It's been completely broken from the start. folio_mk_pmd() should never have been used. Apart from that, the end results LGTM, thanks -- Cheers, David