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 56311272E6D; Fri, 28 Aug 2026 13:39:20 +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=1787924361; cv=none; b=VwXUCTgCfrZhTFpgSkjSeU9IQ6vwZl9OgukdJAlxbbQmpF1zfUNfSjBXv9KzsDAQHWtdtWlhCyU5O/QcTaWj9EoXhRFaiBdQg6V+hzlHC75DP7tXQwOihO/FaXtACjUy1IleRKuXYjOsYEANflCk+kSoscMa5uVuqbW/Do9lZ24= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787924361; c=relaxed/simple; bh=UDzbpoVq0MdOJNJU1faG5NfTStM8urjNnUUbYjLhJjg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UojNBX10b3OY/V0S17QuctbLGbJGdqZBN1JZnnGVM0rYdN1su6kG9YM81teUVhp1p5JKQeyBiMvkvZndnTHOLqjoqeZ6sIZlZTvv/ETNt2vMVKneJyAsA9/hCB8WHkCza8zf1rMKxd29yf/taJ8ayBVGTrbv2N0x41FEi899xiQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IPyEOCE+; 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="IPyEOCE+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2401F1F000E9; Fri, 28 Aug 2026 13:39:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787924360; bh=b0hzVh3T1ie/l+echYOTxDwBFiYljL9L1zhrFVNqVTU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=IPyEOCE+wJogby2iD7btLPv5bw8L2eSwAF0KHaqkK0cfSy++TZ2YhnUeGXLr7Q60p ZpvU2Js7ig2hmZQGCpxYBCbWlDS8XMs2YFmQhw12xx30gJAHz4WMwsB638JcYZxDfF 2NKhPDdZoXz704AcHNc0Zksan9xGkPURKKivPeNJxUiDOvVqMdWu5sPmBKtrnnuW2k ZLDuMozhaEsW9yMJL3mL0Ah+GtdL76pOrNnIF5pmnFdCSn4iwqezJ+L1RbtHqgtKCu +bilRr4Z0srOH7haNjhDuSpceGVAcG3CeWKszQEH5XXx86B7p5uaHzOitzDr71Nvwm o3E2yudiEHCNA== Message-ID: <5e09ebb1-5dc9-44ce-b997-3b545db727cb@kernel.org> Date: Fri, 28 Aug 2026 15:39:15 +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] mm/mremap: account mm->locked_vm correctly for MREMAP_DONTUNMAP To: "Lorenzo Stoakes (ARM)" , Andrew Morton , "Liam R. Howlett" , Jann Horn , Pedro Falcato Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, sashiko-bot , Kunwu Chan , stable@vger.kernel.org References: <20260828-mremap-fix-locked-vm-v1-1-c80be7505d1e@kernel.org> From: "Vlastimil Babka (SUSE)" Content-Language: en-US Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20260828-mremap-fix-locked-vm-v1-1-c80be7505d1e@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/28/26 13:20, Lorenzo Stoakes (ARM) wrote: > When a VMA is mremap()'d with MREMAP_DONTUNMAP set, that results in the VMA > being copied, but the source VMA not being unmapped. > > If the VMA is mlock()'d this is a legal operation, though the source VMA > has its VMA_LOCKED_BIT cleared. > > However this is done in dontunmap_complete(), after mm->locked_vm was > incremented via vrm_stat_account(), resulting in double-counting. > > Worse, this is not even corrected when source VMA is unmapped, due to > the VMA_LOCKED_BIT flag having been cleared. > > This all works fine in the usual mremap() case (without MREMAP_DONTUNMAP), > as the source VMA is unmapped with VMA_LOCKED_BIT intact, at which time > mm->locked_vm is decremented accordingly. > > Resolve the issue by invoking vrm_stat_account() only after > dontunmap_complete() has run. > > Note that MREMAP_DONTUNMAP requires old_len == new_len, so no need to > account for a delta in size in this case. > > The bug was introduced by commit b714ccb02a76 ("mm/mremap: complete > refactor of move_vma()") which incorrectly reordered the accounting and the > clearing of the VMA_LOCKED_BIT flag. > > Reported-by: sashiko-bot > Closes: https://sashiko.dev/#/patchset/20260825-fix-mremap-dontunmap-pgoff-v1-1-39a40b2c98b3@kernel.org > Reported-by: Kunwu Chan > Closes: https://lore.kernel.org/all/20260828094823.594279-1-kunwu.chan@linux.dev/ > Fixes: b714ccb02a76 ("mm/mremap: complete refactor of move_vma()") > Cc: stable@vger.kernel.org > Signed-off-by: Lorenzo Stoakes (ARM) Acked-by: Vlastimil Babka (SUSE) > --- > mm/mremap.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/mm/mremap.c b/mm/mremap.c > index 2b4b523a86b8..7c368440fafe 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -1355,12 +1355,11 @@ static void dontunmap_complete(struct vma_remap_struct *vrm, > if (vma_is_anonymous(vma) && !vma->vm_file) > vma_set_pgoff(vma, pgoff_unfaulted); > } > - > - /* Because we won't unmap we don't need to touch locked_vm. */ > } > > static unsigned long move_vma(struct vma_remap_struct *vrm) > { > + const bool is_dontunmap = vrm->flags & MREMAP_DONTUNMAP; > struct mm_struct *mm = current->mm; > struct vm_area_struct *new_vma; > unsigned long hiwater_vm; > @@ -1401,10 +1400,10 @@ static unsigned long move_vma(struct vma_remap_struct *vrm) > */ > hiwater_vm = mm->hiwater_vm; > > - vrm_stat_account(vrm, vrm->new_len); > - if (unlikely(!err && (vrm->flags & MREMAP_DONTUNMAP))) > + if (unlikely(is_dontunmap && !err)) > dontunmap_complete(vrm, new_vma); > - else > + vrm_stat_account(vrm, vrm->new_len); > + if (!is_dontunmap || err) > unmap_source_vma(vrm); > > mm->hiwater_vm = hiwater_vm; > > --- > base-commit: aeddb4d52acfcc5ce5e988acd48f2906fe966ca3 > change-id: 20260828-mremap-fix-locked-vm-b8991ffc4181 > > Best regards,