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t=1787850327; bh=I1lufsy6Im7NFt6gh/akpxHBSyR/Rxm6eWceVNKlW2g=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=TACTRK+IOCMglSMFUPOyndXcTKYnKOgh5FybKkMq9h/FnqoOsf9eibohXzbUoE6kI U+Wk5sA6pKUcf/AmHtw8iWWcCDMPMSjPfikBDWpYsUEFq9xru871uaWIyNMdyfqLxL nku5/C9TzWJM+SzPhRFKwtMfhiOZcK1YDPftnwG6+LxoCw6qRPCkoGAFSuWVSteog3 z+C0wenTac1qFktXGT5JHIBRsbhkgCl8tDM/UVsbmEKyMY+rCQOuzfkKdrQd4fPSsq 8+0U27G5Mt66hdxlP/t/3pk/MWFCTkUOJNnPZ4QVW+qXaY6FpMnmvrVSkAtyFZE5EM 61Sr2IH44g4ug== Message-ID: <6d855beb-1d24-4a6e-ae62-ac9e05e358e5@kernel.org> Date: Thu, 27 Aug 2026 19:05:21 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/mempolicy: use vm_normal_folio_pmd() in queue_folios_pmd() To: Gregory Price , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, liam@infradead.org, ljs@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, ying.huang@linux.alibaba.com, apopple@nvidia.com, peterx@redhat.com, jgg@ziepe.ca, sashiko-bot , stable@vger.kernel.org References: <20260821144947.167382-1-gourry@gourry.net> <20260821144947.167382-2-gourry@gourry.net> 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-Rspam-User: X-Stat-Signature: 68u8kcmof51mm6uftnferw1zknakamet X-Rspamd-Queue-Id: EA70414001A X-Rspamd-Server: rspam06 X-HE-Tag: 1787850328-823417 X-HE-Meta: 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 dJl6Qukw 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/21/26 16:49, Gregory Price wrote: > 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 I think this is best written as: folio = vm_normal_folio_pmd(walk->vma, addr, pmdval); if (!folio) { if (is_huge_zero_pmd(pmdval)) { walk->action = ACTION_CONTINUE; return; } return; } That way we minimize checks on the expected path. Acked-by: David Hildenbrand (Arm) -- Cheers, David