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[2003:d8:2f1a:3700:2982:b5f7:a04e:4cb4]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-3a568b28240sm1774029f8f.72.2025.06.13.02.27.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 13 Jun 2025 02:27:07 -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 , Oscar Salvador , Jason Gunthorpe Subject: [PATCH v3 2/3] mm/huge_memory: don't mark refcounted folios special in vmf_insert_folio_pmd() Date: Fri, 13 Jun 2025 11:27:01 +0200 Message-ID: <20250613092702.1943533-3-david@redhat.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250613092702.1943533-1-david@redhat.com> References: <20250613092702.1943533-1-david@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: EfCeO3oXtmZILnXTLPZAQNCIfAWSrsBZeiXL-vlJos0_1749806828 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 9CA164000C X-Stat-Signature: 19sja57oa1tj46er1ado5hd98xwme74m X-Rspam-User: X-HE-Tag: 1749806833-618011 X-HE-Meta: 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 /e0rRS17 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Marking PMDs that map a "normal" refcounted folios as special is against our rules documented for vm_normal_page(): normal (refcounted) folios shall never have the page table mapping marked as special. 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 teaching insert_pfn_pmd() to properly handle folios and pfns -- moving refcount/mapcount/etc handling in there, renaming it to insert_pmd(), and distinguishing between both cases using a new simple "struct folio_or_pfn" structure. Use folio_mk_pmd() to create a pmd for a folio cleanly. Fixes: 6c88f72691f8 ("mm/huge_memory: add vmf_insert_folio_pmd()") Reviewed-by: Jason Gunthorpe Reviewed-by: Lorenzo Stoakes Reviewed-by: Dan Williams Tested-by: Dan Williams Signed-off-by: David Hildenbrand --- mm/huge_memory.c | 59 ++++++++++++++++++++++++++++++++---------------- 1 file changed, 40 insertions(+), 19 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 49b98082c5401..d1e3e253c714a 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1372,9 +1372,17 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf) return __do_huge_pmd_anonymous_page(vmf); } -static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, - pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write, - pgtable_t pgtable) +struct folio_or_pfn { + union { + struct folio *folio; + pfn_t pfn; + }; + bool is_folio; +}; + +static int insert_pmd(struct vm_area_struct *vma, unsigned long addr, + pmd_t *pmd, struct folio_or_pfn fop, pgprot_t prot, + bool write, pgtable_t pgtable) { struct mm_struct *mm = vma->vm_mm; pmd_t entry; @@ -1382,8 +1390,11 @@ static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, lockdep_assert_held(pmd_lockptr(mm, pmd)); if (!pmd_none(*pmd)) { + const unsigned long pfn = fop.is_folio ? folio_pfn(fop.folio) : + pfn_t_to_pfn(fop.pfn); + if (write) { - if (pmd_pfn(*pmd) != pfn_t_to_pfn(pfn)) { + if (pmd_pfn(*pmd) != pfn) { WARN_ON_ONCE(!is_huge_zero_pmd(*pmd)); return -EEXIST; } @@ -1396,11 +1407,20 @@ static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, return -EEXIST; } - entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); - if (pfn_t_devmap(pfn)) - entry = pmd_mkdevmap(entry); - else - entry = pmd_mkspecial(entry); + if (fop.is_folio) { + entry = folio_mk_pmd(fop.folio, vma->vm_page_prot); + + folio_get(fop.folio); + folio_add_file_rmap_pmd(fop.folio, &fop.folio->page, vma); + add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR); + } else { + entry = pmd_mkhuge(pfn_t_pmd(fop.pfn, prot)); + + if (pfn_t_devmap(fop.pfn)) + entry = pmd_mkdevmap(entry); + else + entry = pmd_mkspecial(entry); + } if (write) { entry = pmd_mkyoung(pmd_mkdirty(entry)); entry = maybe_pmd_mkwrite(entry, vma); @@ -1431,6 +1451,9 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write) unsigned long addr = vmf->address & PMD_MASK; struct vm_area_struct *vma = vmf->vma; pgprot_t pgprot = vma->vm_page_prot; + struct folio_or_pfn fop = { + .pfn = pfn, + }; pgtable_t pgtable = NULL; spinlock_t *ptl; int error; @@ -1458,8 +1481,8 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write) pfnmap_setup_cachemode_pfn(pfn_t_to_pfn(pfn), &pgprot); ptl = pmd_lock(vma->vm_mm, vmf->pmd); - error = insert_pfn_pmd(vma, addr, vmf->pmd, pfn, pgprot, write, - pgtable); + error = insert_pmd(vma, addr, vmf->pmd, fop, pgprot, write, + pgtable); spin_unlock(ptl); if (error && pgtable) pte_free(vma->vm_mm, pgtable); @@ -1474,6 +1497,10 @@ 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; + struct folio_or_pfn fop = { + .folio = folio, + .is_folio = true, + }; spinlock_t *ptl; pgtable_t pgtable = NULL; int error; @@ -1491,14 +1518,8 @@ vm_fault_t vmf_insert_folio_pmd(struct vm_fault *vmf, struct folio *folio, } ptl = pmd_lock(mm, vmf->pmd); - if (pmd_none(*vmf->pmd)) { - folio_get(folio); - folio_add_file_rmap_pmd(folio, &folio->page, vma); - add_mm_counter(mm, mm_counter_file(folio), HPAGE_PMD_NR); - } - error = insert_pfn_pmd(vma, addr, vmf->pmd, - pfn_to_pfn_t(folio_pfn(folio)), vma->vm_page_prot, - write, pgtable); + error = insert_pmd(vma, addr, vmf->pmd, fop, vma->vm_page_prot, + write, pgtable); spin_unlock(ptl); if (error && pgtable) pte_free(mm, pgtable); -- 2.49.0