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 A614D2749E6; Wed, 8 Jul 2026 13:10:37 +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=1783516239; cv=none; b=T7DCwpaPpqaYeirjKPJIi52oQkE5j1RLRmY3bCKTYEpHdS8mQ5i27oUSApO30iTdpfFXYx0ptccj5BRMVc+UzhBsq7zzASDoiFK7CEhQXXXPbC8iurNPNyz6B2pYARqjOsuH1jq7zUEUUTQfgQ8iz4QYvbMqaSfuJIjWFfdJl0o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783516239; c=relaxed/simple; bh=bVPE4zsNgkKpefdLoNfBb49FFgM1FAOs59suGh2PYSI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=CA48uKkxj/c6xK/dUqC0Kd5LKdElZPfT6lrUe++GY4KrI8W60+mj28/7wXa6wC6b0bFeSGl5rQ+VPHAyDLcq/9picWJlZEG2aVeNX5p8q+dSNjdX7OcccjKwVf5OhAPuGP8mHCO/Zg0HZgAiteLebxpaHn1diGwuZSK0uRanAMo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=X0+8cPel; 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="X0+8cPel" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C7C5D1F000E9; Wed, 8 Jul 2026 13:10:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783516237; bh=XVbR6znNF637T9MAgobLVmsZoz7qMXfdjHyuLiDhLeU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=X0+8cPelmsVUM1oV9qfkrrvutBumdGTkzTk5XjIq+6Nxv952UFEV0WE1hwFN/lEdR thDgQXiPP0LZ3ythiiSua63U9+jgwV4dcluGeGF3H9+1zWP3x22hKA6K3gPSkkiAij 2vd5CvcgynxmGndas4FjOEyBbjEf0tUGGzUdsG5i2Ert4NSKokmzxDzQjBmZG9mirr sUmPtCRbrFovnNg4CImiBzuRY8tQEJOYgYcMUfXE2saapFJ+xArHATO7Dn4BS4AzGu b5a+YZtS2JchD3P4W+SG86maqmyD8WWY0dkcO7fArhaLENrvXiOulr1fFY4Ona1mCT l0vop9xiE7cEQ== Message-ID: Date: Wed, 8 Jul 2026 15:10:28 +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 v2 2/3] mm/madvise: skip device-private PMDs in cold and pageout walks To: Usama Arif , Andrew Morton , apopple@nvidia.com, balbirs@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, 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, ljs@kernel.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 Cc: sashiko-bot , stable@vger.kernel.org References: <20260708122040.861335-1-usama.arif@linux.dev> <20260708122040.861335-3-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 7/8/26 14:20, Usama Arif wrote: > madvise_cold_or_pageout_pte_range() takes pmd_trans_huge_lock(), whose > pmd_is_huge() check returns true for a device-private PMD. The subsequent > !pmd_present() branch has a VM_BUG_ON() asserting migration is the only > allowed non-present case; a device-private PMD trips it. > > Allow device-private PMDs in that non-present assertion and continue to > huge_unlock before calling pmd_folio(). This keeps the assertion for > unexpected PMD softleafs while skipping device-private PMDs like other > non-present PMDs in this path. > > Potential trigger: an HMM-based GPU driver races with > madvise(MADV_COLD)/MADV_PAGEOUT: pmd_trans_huge(*pmd) reads true, then > migrate_vma_pages() flips the PMD to a device-private entry before the > PMD lock is acquired. > > Reported-by: sashiko-bot > Link: https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linux.dev?part=6 > Fixes: 368076f52ebe ("mm/huge_memory: add device-private THP support to PMD operations") > Cc: > Reviewed-by: Joshua Hahn > Reviewed-by: Zi Yan > Reviewed-by: Balbir Singh > Signed-off-by: Usama Arif > --- > mm/madvise.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/madvise.c b/mm/madvise.c > index 9292f60b19aa..1065b5a84ea7 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -389,7 +389,8 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, > > if (unlikely(!pmd_present(orig_pmd))) { > VM_BUG_ON(thp_migration_supported() && > - !pmd_is_migration_entry(orig_pmd)); > + !pmd_is_migration_entry(orig_pmd) && > + !pmd_is_device_private_entry(orig_pmd)); thp_migration_supported() is just effectively CONFIG_TRANSPARENT_HUGEPAGE && CONFIG_ARCH_HAS_PMD_SOFTLEAVES. pmd_is_migration_entry() -> softleaf_is_migration(softleaf_from_pmd(pmd)) == false without CONFIG_ARCH_HAS_PMD_SOFTLEAVES. ... and CONFIG_ARCH_HAS_PMD_SOFTLEAVES is only selected if TRANSPARENT_HUGEPAGE. While at it, can you drop the thp_migration_supported() check and turn the VM_BUG_ON into a VM_WARN_ON_ONCE() ? -- Cheers, David