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[2003:d8:2f0d:f000:eec9:2b8d:4913:f32a]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-450d7fa21e4sm180154785e9.11.2025.06.03.14.16.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Jun 2025 14:16:38 -0700 (PDT) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, David Hildenbrand , Andrew Morton , Alistair Popple , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Dan Williams Subject: [PATCH v1 1/2] mm/huge_memory: don't mark refcounted pages special in vmf_insert_folio_pmd() Date: Tue, 3 Jun 2025 23:16:33 +0200 Message-ID: <20250603211634.2925015-2-david@redhat.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250603211634.2925015-1-david@redhat.com> References: <20250603211634.2925015-1-david@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Marking PMDs that map a "normal" refcounted folios as special is against our rules documented for vm_normal_page(). Fortunately, there are not that many pmd_special() check that can be mislead, and most vm_normal_page_pmd()/vm_normal_folio_pmd() users that would get this wrong right now are rather harmless: e.g., none so far bases decisions whether to grab a folio reference on that decision. Well, and GUP-fast will fallback to GUP-slow. All in all, so far no big implications as it seems. Getting this right will get more important as we use folio_normal_page_pmd() in more places. Fix it by just inlining the relevant code, making the whole pmd_none() handling cleaner. We can now use folio_mk_pmd(). While at it, make sure that a pmd that is not-none is actually present before comparing PFNs. Fixes: 6c88f72691f8 ("mm/huge_memory: add vmf_insert_folio_pmd()") Signed-off-by: David Hildenbrand --- mm/huge_memory.c | 39 ++++++++++++++++++++++++++++++++------- 1 file changed, 32 insertions(+), 7 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index d3e66136e41a3..f9e23dfea76f8 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1474,9 +1474,10 @@ vm_fault_t vmf_insert_folio_pmd(struct vm_fault *vmf, struct folio *folio, struct vm_area_struct *vma = vmf->vma; unsigned long addr = vmf->address & PMD_MASK; struct mm_struct *mm = vma->vm_mm; + pmd_t *pmd = vmf->pmd; spinlock_t *ptl; pgtable_t pgtable = NULL; - int error; + pmd_t entry; if (addr < vma->vm_start || addr >= vma->vm_end) return VM_FAULT_SIGBUS; @@ -1490,17 +1491,41 @@ vm_fault_t vmf_insert_folio_pmd(struct vm_fault *vmf, struct folio *folio, return VM_FAULT_OOM; } - ptl = pmd_lock(mm, vmf->pmd); - if (pmd_none(*vmf->pmd)) { + ptl = pmd_lock(mm, pmd); + if (pmd_none(*pmd)) { folio_get(folio); folio_add_file_rmap_pmd(folio, &folio->page, vma); add_mm_counter(mm, mm_counter_file(folio), HPAGE_PMD_NR); + + entry = folio_mk_pmd(folio, vma->vm_page_prot); + if (write) { + entry = pmd_mkyoung(pmd_mkdirty(entry)); + entry = maybe_pmd_mkwrite(entry, vma); + } + set_pmd_at(mm, addr, pmd, entry); + update_mmu_cache_pmd(vma, addr, pmd); + + if (pgtable) { + pgtable_trans_huge_deposit(mm, pmd, pgtable); + mm_inc_nr_ptes(mm); + pgtable = NULL; + } + } else if (pmd_present(*pmd) && write) { + /* + * We only allow for upgrading write permissions if the + * same folio is already mapped. + */ + if (pmd_pfn(*pmd) == folio_pfn(folio)) { + entry = pmd_mkyoung(*pmd); + entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); + if (pmdp_set_access_flags(vma, addr, pmd, entry, 1)) + update_mmu_cache_pmd(vma, addr, pmd); + } else { + WARN_ON_ONCE(!is_huge_zero_pmd(*pmd)); + } } - error = insert_pfn_pmd(vma, addr, vmf->pmd, - pfn_to_pfn_t(folio_pfn(folio)), vma->vm_page_prot, - write, pgtable); spin_unlock(ptl); - if (error && pgtable) + if (pgtable) pte_free(mm, pgtable); return VM_FAULT_NOPAGE; -- 2.49.0