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h=Date:From:To:Cc:Subject:References:In-Reply-To; b=FzsOqxB7yjmk8r6CDB1CdPdVSUYM1meVTyG+V/ZCtyKyIxP8e+cqryo0Fr21Vhz3f 66ASdWOyx/Ehv096Cid8xYzpM1MdYGKW5fuzjrbhydwKrjLdjaqZDw9vHOM8JXFOfs rUOUC/QVGHsS23/kpeM0sWl//ckJbBvai8EZtdI0+4DHZ+IG0zxx96PzUqIdqj698B 2dqdoTX2/qf7Ej4kKrxD7mipggBuyjgxRIeyg1015ogfpjPZnoEdMcgkn7A3tZovYc trvndunLLmVIFkvPHKnMACJkgKn7DEYriLNwEC9kSWhUwV09GEOaDBA6/y86oy5VPK gSCC9MZQaC7Sw== Date: Sat, 11 Jul 2026 09:13:44 +0100 From: Lorenzo Stoakes To: Usama Arif Cc: Andrew Morton , baohua@kernel.org, baolin.wang@linux.alibaba.com, david@kernel.org, dev.jain@arm.com, lance.yang@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.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, sashiko-bot Subject: Re: [PATCH] userfaultfd: wait on source PMD during UFFDIO_MOVE Message-ID: References: <20260705131231.1499198-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260705131231.1499198-1-usama.arif@linux.dev> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: EBABA10000A X-Stat-Signature: ja1uedb4tbjkckeyxc8bi3rt8uiz8qem X-HE-Tag: 1783757638-443390 X-HE-Meta: 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 H6RVXox2 XLdvXfHoPkUDUDcxpiz6b0J7i7Snxfkuyow4caEEXwJjjuMrWvagFWymb07FXRzfmJcRsmPVHZMr8OJ22uk06okEUmARwnVuT774e9G/rVQjpFb9elL2DWJ7Q8rOiqUWoLrEFF2SpbyGFygFOsZcGsCtpsw0XFGgnYZUr+nuuc9qEOguqPm6zGCJ3c578qrZa8kAFO+++aTFtzaIyLl0eqsqU6pcg8CrleJh0Nat43JjRgqael0ByFBbnNxm3RKh7qlB2MvScBwVDqjHKyhshCKbCpVMIYrMHKZr2I7NGUTvV1O2LNsvadSBHsn8+6wZ2TH10sof43Hv5wlmRP1EjVoAzaSKk+1ibO2GNGOwy4apy+ZiZcuz0W3pLzDO5J6b3E0WZ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Jul 05, 2026 at 06:12:31AM -0700, 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. Yikes! > > 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 LGTM so: Reviewed-by: Lorenzo Stoakes > --- > 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; > -- > 2.53.0-Meta > Cheers, Lorenzo