From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 F39F83F4DD0 for ; Mon, 6 Jul 2026 09:01:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783328468; cv=none; b=PnF9Bt2pDnhqWsEl260A3cVRo4YaaQXEl/g1qTuNvGcEFF/l8OW2LZgnfYlAA9TyPetR4ldSlTC6UbDsYNi6u/fUwZZOJqOCvPoE3CDYjNogO6zIDW0W8QXGxpv/55VcKPuD2sXX1McLJbAsRF/YCHUd5KEcbXSU3MnjB06sYOU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783328468; c=relaxed/simple; bh=8ykZgbO2XUlLio8cTvYB1zIeanpWVuzn66XbskqqH8o=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XIaBP0XY0tTXfgE5Wm8xzWzb2iGR4P4FbBY7foGzgtq/nYl5A1X3aJhpGM2dBfPnshv7HTxQ+bWsew0ec6cXwZzMrXLj19uIDRG6g4zQZgw9r+ecMZHhytFquyML15yevdQINPyKBIzO6pmV3idOhOUf1KAgD+DEmYzjw1aBv1w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FwoRmujM; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="FwoRmujM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 112BF1F000E9; Mon, 6 Jul 2026 09:00:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783328460; bh=Y2p8nkhKN8t9mp7pTmf6Ynt4ux072QpIkTobc4ZCA18=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=FwoRmujMe0ome16BLJ1D9b/TMcpeiIFUYp2tOrucgFjRkQnsLoRRy+gVwGwz0lqpE gnCbDR7KeGd33Vybq/kdL73A3Q5YE1YPSt4y9nWmf+4yKY23cUeEZ0jK5hugA/V2BM n/lmz0Q5WUiQB3FsIrl3vM9vgx7QjaWWpk0HraESZhimqgPh2iOgYBn5vdZcFLJPKL /jGe1RqTf+uR0vORchLLNzz3YnK7obP+U8RcMgNM+KkPwcK0BAio3yL9eZqvRHo4/X qBPLI2aODq/zvKv7qCwZEhrrFmfOmpFA+l/e8EMw5X9hKunnZ6YKVC/VDWaG8R++ry HMFNkLNe6SONg== Message-ID: <461b067f-6fa4-4539-882f-1ee6fbca5583@kernel.org> Date: Mon, 6 Jul 2026 11:00:53 +0200 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] userfaultfd: wait on source PMD during UFFDIO_MOVE To: Usama Arif , Andrew Morton , baohua@kernel.org, baolin.wang@linux.alibaba.com, dev.jain@arm.com, lance.yang@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, npache@redhat.com, ryan.roberts@arm.com, ziy@nvidia.com, aarcange@redhat.com, shakeel.butt@linux.dev, hannes@cmpxchg.org, riel@surriel.com, kernel-team@meta.com Cc: sashiko-bot References: <20260705131231.1499198-1-usama.arif@linux.dev> 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 7/5/26 15:12, Usama Arif wrote: > move_pages_huge_pmd() snapshots src_pmdval under src_ptl, drops the lock, > and, for migration entries, waits with pmd_migration_entry_wait(). > > Passing &src_pmdval is wrong. pmd_migration_entry_wait() must lock and > re-read the real page-table PMD; on split-PMD-lock kernels, a stack > address also resolves to the wrong lock. softleaf_entry_wait_on_locked() > then waits without a folio reference, which is safe only while serialized > against migration-entry removal by the real PT lock. > > Pass src_pmd, matching __handle_mm_fault() and hmm_vma_walk_pmd(). > > Reported-by: sashiko-bot > Link: https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linux.dev?part=8 > Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") > Signed-off-by: Usama Arif > --- > 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 bdd8635922f9..c0892cc533a9 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2775,7 +2775,7 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm > if (!pmd_trans_huge(src_pmdval)) { > spin_unlock(src_ptl); > if (pmd_is_migration_entry(src_pmdval)) { > - pmd_migration_entry_wait(mm, &src_pmdval); > + pmd_migration_entry_wait(mm, src_pmd); > return -EAGAIN; > } > return -ENOENT; Looks good and follows roughly what we do in __handle_mm_fault(). Acked-by: David Hildenbrand (Arm) -- Cheers, David