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Message-ID: <20250611120654.545963-4-david@redhat.com>
Date: Wed, 11 Jun 2025 14:06:54 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
nvdimm@...ts.linux.dev,
linux-cxl@...r.kernel.org,
David Hildenbrand <david@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Alistair Popple <apopple@...dia.com>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>,
Mike Rapoport <rppt@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>,
Michal Hocko <mhocko@...e.com>,
Zi Yan <ziy@...dia.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Nico Pache <npache@...hat.com>,
Ryan Roberts <ryan.roberts@....com>,
Dev Jain <dev.jain@....com>,
Dan Williams <dan.j.williams@...el.com>,
Oscar Salvador <osalvador@...e.de>
Subject: [PATCH v2 3/3] mm/huge_memory: don't mark refcounted folios special in vmf_insert_folio_pud()
Marking PUDs that map a "normal" refcounted folios as special is
against our rules documented for vm_normal_page().
Fortunately, there are not that many pud_special() check that can be
mislead and are right now 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 introduce
folio_normal_page_pud() and start using it in more place where we
currently special-case based on other VMA flags.
Fix it just like we fixed vmf_insert_folio_pmd().
Add folio_mk_pud() to mimic what we do with folio_mk_pmd().
Fixes: dbe54153296d ("mm/huge_memory: add vmf_insert_folio_pud()")
Signed-off-by: David Hildenbrand <david@...hat.com>
---
include/linux/mm.h | 19 ++++++++++++++++-
mm/huge_memory.c | 51 +++++++++++++++++++++++++---------------------
2 files changed, 46 insertions(+), 24 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index fa538feaa8d95..912b6d40a12d6 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1816,7 +1816,24 @@ static inline pmd_t folio_mk_pmd(struct folio *folio, pgprot_t pgprot)
{
return pmd_mkhuge(pfn_pmd(folio_pfn(folio), pgprot));
}
-#endif
+
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
+/**
+ * folio_mk_pud - Create a PUD for this folio
+ * @folio: The folio to create a PUD for
+ * @pgprot: The page protection bits to use
+ *
+ * Create a page table entry for the first page of this folio.
+ * This is suitable for passing to set_pud_at().
+ *
+ * Return: A page table entry suitable for mapping this folio.
+ */
+static inline pud_t folio_mk_pud(struct folio *folio, pgprot_t pgprot)
+{
+ return pud_mkhuge(pfn_pud(folio_pfn(folio), pgprot));
+}
+#endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
#endif /* CONFIG_MMU */
static inline bool folio_has_pincount(const struct folio *folio)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7e3e9028873e5..4734de1dc0ae4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1535,15 +1535,18 @@ static pud_t maybe_pud_mkwrite(pud_t pud, struct vm_area_struct *vma)
return pud;
}
-static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
- pud_t *pud, pfn_t pfn, pgprot_t prot, bool write)
+static void insert_pud(struct vm_area_struct *vma, unsigned long addr,
+ pud_t *pud, struct folio_or_pfn fop, pgprot_t prot, bool write)
{
struct mm_struct *mm = vma->vm_mm;
pud_t entry;
if (!pud_none(*pud)) {
+ const unsigned long pfn = fop.is_folio ? folio_pfn(fop.folio) :
+ pfn_t_to_pfn(fop.pfn);
+
if (write) {
- if (WARN_ON_ONCE(pud_pfn(*pud) != pfn_t_to_pfn(pfn)))
+ if (WARN_ON_ONCE(pud_pfn(*pud) != pfn))
return;
entry = pud_mkyoung(*pud);
entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma);
@@ -1553,11 +1556,19 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
return;
}
- entry = pud_mkhuge(pfn_t_pud(pfn, prot));
- if (pfn_t_devmap(pfn))
- entry = pud_mkdevmap(entry);
- else
- entry = pud_mkspecial(entry);
+ if (fop.is_folio) {
+ entry = folio_mk_pud(fop.folio, vma->vm_page_prot);
+
+ folio_get(fop.folio);
+ folio_add_file_rmap_pud(fop.folio, &fop.folio->page, vma);
+ add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PUD_NR);
+ } else {
+ entry = pud_mkhuge(pfn_t_pud(fop.pfn, prot));
+ if (pfn_t_devmap(fop.pfn))
+ entry = pud_mkdevmap(entry);
+ else
+ entry = pud_mkspecial(entry);
+ }
if (write) {
entry = pud_mkyoung(pud_mkdirty(entry));
entry = maybe_pud_mkwrite(entry, vma);
@@ -1581,6 +1592,9 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write)
unsigned long addr = vmf->address & PUD_MASK;
struct vm_area_struct *vma = vmf->vma;
pgprot_t pgprot = vma->vm_page_prot;
+ struct folio_or_pfn fop = {
+ .pfn = pfn,
+ };
spinlock_t *ptl;
/*
@@ -1600,7 +1614,7 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write)
pfnmap_setup_cachemode_pfn(pfn_t_to_pfn(pfn), &pgprot);
ptl = pud_lock(vma->vm_mm, vmf->pud);
- insert_pfn_pud(vma, addr, vmf->pud, pfn, pgprot, write);
+ insert_pud(vma, addr, vmf->pud, fop, pgprot, write);
spin_unlock(ptl);
return VM_FAULT_NOPAGE;
@@ -1622,6 +1636,10 @@ vm_fault_t vmf_insert_folio_pud(struct vm_fault *vmf, struct folio *folio,
unsigned long addr = vmf->address & PUD_MASK;
pud_t *pud = vmf->pud;
struct mm_struct *mm = vma->vm_mm;
+ struct folio_or_pfn fop = {
+ .folio = folio,
+ .is_folio = true,
+ };
spinlock_t *ptl;
if (addr < vma->vm_start || addr >= vma->vm_end)
@@ -1631,20 +1649,7 @@ vm_fault_t vmf_insert_folio_pud(struct vm_fault *vmf, struct folio *folio,
return VM_FAULT_SIGBUS;
ptl = pud_lock(mm, pud);
-
- /*
- * If there is already an entry present we assume the folio is
- * already mapped, hence no need to take another reference. We
- * still call insert_pfn_pud() though in case the mapping needs
- * upgrading to writeable.
- */
- if (pud_none(*vmf->pud)) {
- folio_get(folio);
- folio_add_file_rmap_pud(folio, &folio->page, vma);
- add_mm_counter(mm, mm_counter_file(folio), HPAGE_PUD_NR);
- }
- insert_pfn_pud(vma, addr, vmf->pud, pfn_to_pfn_t(folio_pfn(folio)),
- vma->vm_page_prot, write);
+ insert_pud(vma, addr, vmf->pud, fop, vma->vm_page_prot, write);
spin_unlock(ptl);
return VM_FAULT_NOPAGE;
--
2.49.0
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