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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93720493f35sm609512385a.9.2026.08.21.07.50.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Aug 2026 07:50:06 -0700 (PDT) From: Gregory Price To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, liam@infradead.org, ljs@kernel.org, david@kernel.org, vbabka@kernel.org, jannh@google.com, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, peterx@redhat.com, jgg@ziepe.ca, sashiko-bot , stable@vger.kernel.org Subject: [PATCH 1/2] mm/mempolicy: use vm_normal_folio_pmd() in queue_folios_pmd() Date: Fri, 21 Aug 2026 10:49:46 -0400 Message-ID: <20260821144947.167382-2-gourry@gourry.net> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260821144947.167382-1-gourry@gourry.net> References: <20260821144947.167382-1-gourry@gourry.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit mmap a VM_PFNMAP region whose ->huge_fault installs a PMD through vmf_insert_pfn_pmd() - a vfio-pci MMIO BAR does this - then mbind(p, len, MPOL_BIND, &mask, maxnode, MPOL_MF_STRICT); With a stand-in module for the driver: BUG: unable to handle page fault for address: fffff96dc0000008 RIP: 0010:queue_folios_pte_range+0xaf/0x440 walk_pgd_range+0x52b/0xaf0 __walk_page_range+0x6a/0x1d0 walk_page_range_mm_unsafe+0x193/0x230 queue_pages_range+0x64/0xa0 do_mbind+0x25e/0x640 queue_folios_pmd(), inlined above, calls pmd_folio() on that PMD. The pfn is raw MMIO with no memmap entry, so the folio lands in unpopulated vmemmap. Neither guard stops the walk: walk_page_test() skips VM_PFNMAP, but queue_pages_walk_ops supplies ->test_walk, so it never runs queue_pages_test_walk() honours vma_migratable(), but only while MPOL_MF_STRICT is clear A VM_MIXEDMAP vma needs neither flag, being vma_migratable(), so plain mbind(MPOL_MF_MOVE) reaches this too - and there the bad folio carries on into migrate_folio_add() and folio_isolate_lru(). mshv_vtl_low is such a mapping. Use vm_normal_folio_pmd() and skip on NULL, as the PTE loop in queue_folios_pte_range() already does with vm_normal_folio(). The huge zero PMD moves ahead of the lookup, since vm_normal_folio_pmd() returns NULL for it and its ACTION_CONTINUE would be lost. mbind(MPOL_MF_STRICT) over a PMD mapped VM_PFNMAP region now returns 0 rather than -EIO. The PTE loop already returned 0 there. Fixes: 3c8e44c9b369 ("mm: mark special bits for huge pfn mappings when inject") Reported-by: sashiko-bot Closes: https://sashiko.dev/#/patchset/20260817220810.1175596-1-gourry%40gourry.net Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-5 Signed-off-by: Gregory Price (Meta) --- mm/mempolicy.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index f1aba551f9f1..85803c845965 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -650,7 +650,8 @@ static inline bool queue_folio_required(struct folio *folio, return node_isset(nid, *qp->nmask) == !(flags & MPOL_MF_INVERT); } -static void queue_folios_pmd(pmd_t *pmd, struct mm_walk *walk) +static void queue_folios_pmd(pmd_t *pmd, unsigned long addr, + struct mm_walk *walk) { struct folio *folio; struct queue_pages *qp = walk->private; @@ -661,13 +662,15 @@ static void queue_folios_pmd(pmd_t *pmd, struct mm_walk *walk) qp->nr_failed++; return; } - folio = pmd_folio(pmdval); - if (folio_is_zone_device(folio)) - return; - if (is_huge_zero_folio(folio)) { + if (is_huge_zero_pmd(pmdval)) { walk->action = ACTION_CONTINUE; return; } + folio = vm_normal_folio_pmd(walk->vma, addr, pmdval); + if (!folio) + return; + if (folio_is_zone_device(folio)) + return; if (!queue_folio_required(folio, qp)) return; if (!(qp->flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) || @@ -700,7 +703,7 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr, ptl = pmd_trans_huge_lock(pmd, vma); if (ptl) { - queue_folios_pmd(pmd, walk); + queue_folios_pmd(pmd, addr, walk); spin_unlock(ptl); goto out; } -- 2.55.0