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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 Reviewed-by: Oscar Salvador Reviewed-by: Oscar salvador --- 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_faul= t *vmf) return __do_huge_pmd_anonymous_page(vmf); } =20 -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 =3D 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)); =20 if (!pmd_none(*pmd)) { + const unsigned long pfn =3D fop.is_folio ? folio_pfn(fop.folio) : + pfn_t_to_pfn(fop.pfn); + if (write) { - if (pmd_pfn(*pmd) !=3D pfn_t_to_pfn(pfn)) { + if (pmd_pfn(*pmd) !=3D pfn) { WARN_ON_ONCE(!is_huge_zero_pmd(*pmd)); return -EEXIST; } @@ -1396,11 +1407,20 @@ static int insert_pfn_pmd(struct vm_area_struct *vm= a, unsigned long addr, return -EEXIST; } =20 - entry =3D pmd_mkhuge(pfn_t_pmd(pfn, prot)); - if (pfn_t_devmap(pfn)) - entry =3D pmd_mkdevmap(entry); - else - entry =3D pmd_mkspecial(entry); + if (fop.is_folio) { + entry =3D 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 =3D pmd_mkhuge(pfn_t_pmd(fop.pfn, prot)); + + if (pfn_t_devmap(fop.pfn)) + entry =3D pmd_mkdevmap(entry); + else + entry =3D pmd_mkspecial(entry); + } if (write) { entry =3D pmd_mkyoung(pmd_mkdirty(entry)); entry =3D maybe_pmd_mkwrite(entry, vma); @@ -1431,6 +1451,9 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, p= fn_t pfn, bool write) unsigned long addr =3D vmf->address & PMD_MASK; struct vm_area_struct *vma =3D vmf->vma; pgprot_t pgprot =3D vma->vm_page_prot; + struct folio_or_pfn fop =3D { + .pfn =3D pfn, + }; pgtable_t pgtable =3D NULL; spinlock_t *ptl; int error; @@ -1458,8 +1481,8 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, p= fn_t pfn, bool write) pfnmap_setup_cachemode_pfn(pfn_t_to_pfn(pfn), &pgprot); =20 ptl =3D pmd_lock(vma->vm_mm, vmf->pmd); - error =3D insert_pfn_pmd(vma, addr, vmf->pmd, pfn, pgprot, write, - pgtable); + error =3D 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 =3D vmf->vma; unsigned long addr =3D vmf->address & PMD_MASK; struct mm_struct *mm =3D vma->vm_mm; + struct folio_or_pfn fop =3D { + .folio =3D folio, + .is_folio =3D true, + }; spinlock_t *ptl; pgtable_t pgtable =3D NULL; int error; @@ -1491,14 +1518,8 @@ vm_fault_t vmf_insert_folio_pmd(struct vm_fault *vmf= , struct folio *folio, } =20 ptl =3D 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 =3D insert_pfn_pmd(vma, addr, vmf->pmd, - pfn_to_pfn_t(folio_pfn(folio)), vma->vm_page_prot, - write, pgtable); + error =3D insert_pmd(vma, addr, vmf->pmd, fop, vma->vm_page_prot, + write, pgtable); spin_unlock(ptl); if (error && pgtable) pte_free(mm, pgtable); --=20 2.49.0