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 89F0E14AD20 for ; Tue, 7 Jul 2026 14:02:10 +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=1783432931; cv=none; b=iUdR/etI3FRYFFwiebRBeun8liKA8cJ2fOQJHzQCRkFqUaaS7oivFdHlg/+LP1jR2jrKkf7NgIMzThktt3iLg8ljsVm1lmGkZpnMotGA/TdbioQwvcOXw5vBsXJ3TmanOBMSdg062v3OFfEBhmP+ImZLmwNDsbqxhhQPLy8O3bo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783432931; c=relaxed/simple; bh=kTL2z4664T18Q5y+o/F30osTOwaaLepX57NGjDZ62hQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=a9ZdsgCWEgn25vk3GNEZ7REx4D1fOGqUM82iyriEStO+QCykDB1kqs5vuXOn8ddh7fBsjRJ4kZTgVTYwDMLw3euVojWtWpbxtsW5f7rQdfYMZ5dCNtz/S+DksWsYPcXaIuThUyZK1EdH1qGRaVgaUiY43fF5yFXQRyxE6NBwwKU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WFz4ruk4; 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="WFz4ruk4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4E9B51F00A3D; Tue, 7 Jul 2026 14:02:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783432929; bh=hDE86xd7OeBvi8ecp4Qortake90i1hEVi4Wnjvs+Q8I=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=WFz4ruk4piV93ZQ4huC8JBMurPzadbXIBA3gZMf2h/UfrQ4PUYGgpDnNOitfoHnKy 0IZaX2o0UZyAEAxtFfUhnvFIi4FsKUROzE1lupgV3Xj7A47Am/9RghcUHL2LugTY9V WR7LvrHSyxKxnf/hstrjZDunmuOMpChsRYmgCsgF4VtbvdfF5elrqe84hVLUK1o0ms tGlKWLJB29JeE1NBWoexrOV8H+9Pzla6PHoExwJuDV0gorXz8Nhj28PewUDMX2aWVJ ANs0Yih2cYD24DRXIpDLbNbd2kDtAvdXs40dbU3RiYtHdrmMrxzVT7hXZXEWgeOApQ XOv7H6rcmxNdg== Date: Tue, 7 Jul 2026 15:01:56 +0100 From: Lorenzo Stoakes To: Usama Arif Cc: Andrew Morton , apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, jannh@google.com, joshua.hahnjy@gmail.com, lance.yang@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, matthew.brost@intel.com, npache@redhat.com, rakie.kim@sk.com, ryan.roberts@arm.com, vbabka@kernel.org, ying.huang@linux.alibaba.com, ziy@nvidia.com, shakeel.butt@linux.dev, hannes@cmpxchg.org, Balbir Singh Subject: Re: [PATCH 0/3] mm: handle device-private PMDs in walk callbacks Message-ID: References: <20260707135255.292870-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260707135255.292870-1-usama.arif@linux.dev> +cc Balbir Thanks for the series! I think Balbir should be cc'd no? On Tue, Jul 07, 2026 at 06:45:06AM -0700, Usama Arif wrote: > Since commit 368076f52ebe ("mm/huge_memory: add device-private THP support > to PMD operations") a PMD may hold a device-private swap entry whenever > an HMM-based GPU driver migrates an anonymous THP folio to device memory > via migrate_vma_pages(). > > pmd_trans_huge_lock() succeeds for such PMDs (pmd_is_huge() returns true > for any non-present, non-none huge PMD), so several MM walk callbacks > that used to assume present THP or migration entry are now reachable with > a device-private PMD. The results range from a VM_BUG_ON() firing on debug > kernels, to an oops on a bogus vmemmap dereference, to silently isolating > an unrelated live folio from LRU in the aliasing case. > > The first 2 fixes were reported as pre-existing issues by sashiko in my > PMD swap entry series [1]. Hopefully sashiko won't point these out > in the next PMD swap entry series :) Yeah I don't love these 'existing problem' reports (distracting from other work, add workload, really it feels like that should be a passive reporting mode for sashiko not arbitrarily added to other series), but sending it as a separate series is indeed the right way :) These of course should never block an unrelated series. > > [1] https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linux.dev?part=6 Hmm we've had a whole host of issues with device-private PMDs recently. Balbir - would it be possible to audit all of the code paths and proactively see if there's anything else that could hit problems here? > > Usama Arif (3): > mm/mempolicy: skip device-private PMDs when queueing folios > mm/madvise: skip device-private PMDs in cold and pageout walks > mm/huge_memory: skip device-private PMDs in madvise_free_huge_pmd > > mm/huge_memory.c | 3 +++ > mm/madvise.c | 3 +++ > mm/mempolicy.c | 2 ++ > 3 files changed, 8 insertions(+) > > -- > 2.53.0-Meta > Cheers, Lorenzo