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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 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 X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: F16C420004 X-Stat-Signature: baxmun3yjujc7t1tizaadkxbwfh95jrb X-Rspam-User: X-HE-Tag: 1783516237-785221 X-HE-Meta: U2FsdGVkX1/Iv7Z/2YxxBbwNmnDj5ZXRivBYHp8CATKo59C0/5Z9GyKIGgIYWcwzuMbT4dRADKYp5OZC/hjvsIXHT7+wJ8vx5BJPi7SDuTRyURA4m4pah1HfW/PH9eUn1RegfhcHq78w5DILn8eEskRjV+319Cbnb4lkvO8iT47srquvhW4fVtseZSnPF2v5lTyBRpbEsYtTkJCUdAlCnqYTjSSfptAAG+9ASlns8/WwKhWwLZN3Jnv6ySWS3Noxr4L83CftWm7SwsN5EUBMcpk1maAVEubgDFuOaiJIrj6I1Bax44DvhDd8sOk+dJLAu8nEJ/2PPdYlqBfGctqqYvrQtkLHCfoaZb6M/d6RivHAqUmXN0bJXVWF6xHbcc2CJdvPnSib8A5eakI7lFEs5FZZV017Lgl1KvDFbD2HmrbtDjpT3mlN0INKkOCYaHxd1v4PG9387Dvi1wgQAsvErK3bVN+lrSjieI14Qh7hFs7AVyOR/UGukCdFdGYKEBubIy7hXEZsKuG4JbMVdq4sggppLurbo7YGsjVycxI7jk1lfQmVUttosh7rITGm1igEaRngdZsrjJGAcEzzdcxVMt5jOziIh+27vyuXEzHvyDFyUqy2JAIqy6n33jLrpe/XOuvhxR7E9wsmLulHMV5nGN/TcraYVg/dvu0ge2sj+2pnUKXCf5+y1CIWNXxnXogdFqAUGu93J3lGXe2P0Zx2xhr5tWZlF4vNI1mW3Y3WnBEBGwwaOyY4qZcIeZ9bwq8YbLDhjDtoWvvFXHtpK/RTZJq7nzTTCmSeY/29jRHP2ZlBoIzcODAPANgvugrJJ1ArJLkRlQJfFrxgEmUr6cV0c0ANcUN500we+PVff+b5DJXkgKbSg/JX0cIqbL4q8fLaCNYlcpxm65oWxJo6rPPwId4XEEIxYYcS+zNdnj1fpC9gIcLbk2je4iwtRUL3HuVc+FwalYFkxMWey7OqVXF gGwQY+xg Jrzrqf+CTGls8bxShLJg/CMZEAriMlDoxNGiADH0mQlTh1P1zfIGv17XbPFF+H/7vUkxwxQKyZAfqQhXMvx+FHIkSfAfIv+z6rpn7vuGt7vSwvhW6q6Xer46VIJ0NNkl8FZtnqHdZZ8qASz6I2mO8vORvcS2R0R6kATzP4BQsqHwvijm06r2PPkOzq9WGBlZ9QT9qV/7U0pt6TPSh/6gZTd4a0kwk/hiIhhSyTm8mlHSoPX9SqF/V8MmDScYz9tWRhChVjpnhL4hYWhhyZDc9gzCKCdOqwLFjX/jI08v4GJN54ME/qWl/pJs4EdcCF500hWyZi1ALNrRkrCeFCcW/mdxMUn/p6Sdsk6oMmYnYL7v2FXJJ8WKk45GRZZ80iIzyA3OFal09dOvYhZxG01mS+wThi4D4U/lrUXqsJyHDVuhLRyKlkaHprftswdpSgd5R+MTLjSTZMTAcLbR1DhSlwkr+DQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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