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Message-ID: <20250617154345.2494405-11-david@redhat.com>
Date: Tue, 17 Jun 2025 17:43:41 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org,
nvdimm@...ts.linux.dev,
David Hildenbrand <david@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Juergen Gross <jgross@...e.com>,
Stefano Stabellini <sstabellini@...nel.org>,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
Dan Williams <dan.j.williams@...el.com>,
Alistair Popple <apopple@...dia.com>,
Matthew Wilcox <willy@...radead.org>,
Jan Kara <jack@...e.cz>,
Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>,
Zi Yan <ziy@...dia.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
Nico Pache <npache@...hat.com>,
Ryan Roberts <ryan.roberts@....com>,
Dev Jain <dev.jain@....com>,
Barry Song <baohua@...nel.org>,
Vlastimil Babka <vbabka@...e.cz>,
Mike Rapoport <rppt@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>,
Michal Hocko <mhocko@...e.com>,
Jann Horn <jannh@...gle.com>,
Pedro Falcato <pfalcato@...e.de>
Subject: [PATCH RFC 10/14] mm/memory: factor out common code from vm_normal_page_*()
Let's reduce the code duplication and factor out the non-pte/pmd related
magic into vm_normal_page_pfn().
To keep it simpler, check the pfn against both zero folios. We could
optimize this, but as it's only for the !CONFIG_ARCH_HAS_PTE_SPECIAL
case, it's not a compelling micro-optimization.
With CONFIG_ARCH_HAS_PTE_SPECIAL we don't have to check anything else,
really.
It's a good question if we can even hit the !CONFIG_ARCH_HAS_PTE_SPECIAL
scenario in the PMD case in practice: but doesn't really matter, as
it's now all unified in vm_normal_page_pfn().
While at it, add a check that pmd_special() is really only set where we
would expect it.
No functional change intended.
Signed-off-by: David Hildenbrand <david@...hat.com>
---
mm/memory.c | 104 +++++++++++++++++++++++-----------------------------
1 file changed, 46 insertions(+), 58 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index b6c069f4ad11f..3d3fa01cd217e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -536,6 +536,46 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
}
+/* Called only if the page table entry is not marked special. */
+static inline struct page *vm_normal_page_pfn(struct vm_area_struct *vma,
+ unsigned long addr, unsigned long pfn)
+{
+ /*
+ * With CONFIG_ARCH_HAS_PTE_SPECIAL, any special page table mappings
+ * (incl. shared zero folios) are marked accordingly.
+ */
+ if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL))
+ goto normal_page;
+
+ if (unlikely(vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))) {
+ if (vma->vm_flags & VM_MIXEDMAP) {
+ /* If it has a "struct page", it's "normal". */
+ if (!pfn_valid(pfn))
+ return NULL;
+ } else {
+ unsigned long off = (addr - vma->vm_start) >> PAGE_SHIFT;
+
+ /* Only CoW'ed anon folios are "normal". */
+ if (pfn == vma->vm_pgoff + off)
+ return NULL;
+ if (!is_cow_mapping(vma->vm_flags))
+ return NULL;
+ }
+ }
+
+ if (is_zero_pfn(pfn) || is_huge_zero_pfn(pfn))
+ return NULL;
+
+normal_page:
+ /*
+ * NOTE! We still have PageReserved() pages in the page tables.
+ * For example, VDSO mappings can cause them to exist.
+ */
+ VM_WARN_ON_ONCE(!pfn_valid(pfn));
+ VM_WARN_ON_ONCE(is_zero_pfn(pfn) || is_huge_zero_pfn(pfn));
+ return pfn_to_page(pfn);
+}
+
/*
* vm_normal_page -- This function gets the "struct page" associated with a pte.
*
@@ -591,9 +631,7 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
{
unsigned long pfn = pte_pfn(pte);
- if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) {
- if (likely(!pte_special(pte)))
- goto out;
+ if (unlikely(pte_special(pte))) {
if (vma->vm_ops && vma->vm_ops->find_special_page)
return vma->vm_ops->find_special_page(vma, addr);
if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
@@ -604,34 +642,7 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
print_bad_pte(vma, addr, pte, NULL);
return NULL;
}
-
- /* !CONFIG_ARCH_HAS_PTE_SPECIAL case follows: */
-
- if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
- if (vma->vm_flags & VM_MIXEDMAP) {
- if (!pfn_valid(pfn))
- return NULL;
- } else {
- unsigned long off;
- off = (addr - vma->vm_start) >> PAGE_SHIFT;
- if (pfn == vma->vm_pgoff + off)
- return NULL;
- if (!is_cow_mapping(vma->vm_flags))
- return NULL;
- }
- }
-
- if (is_zero_pfn(pfn))
- return NULL;
-
- /*
- * NOTE! We still have PageReserved() pages in the page tables.
- * eg. VDSO mappings can cause them to exist.
- */
-out:
- VM_WARN_ON_ONCE(!pfn_valid(pfn));
- VM_WARN_ON_ONCE(is_zero_pfn(pfn));
- return pfn_to_page(pfn);
+ return vm_normal_page_pfn(vma, addr, pfn);
}
struct folio *vm_normal_folio(struct vm_area_struct *vma, unsigned long addr,
@@ -650,35 +661,12 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
{
unsigned long pfn = pmd_pfn(pmd);
- /* Currently it's only used for huge pfnmaps */
- if (unlikely(pmd_special(pmd)))
+ if (unlikely(pmd_special(pmd))) {
+ VM_WARN_ON_ONCE(!(vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)) &&
+ !is_huge_zero_pfn(pfn));
return NULL;
-
- if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
- if (vma->vm_flags & VM_MIXEDMAP) {
- if (!pfn_valid(pfn))
- return NULL;
- goto out;
- } else {
- unsigned long off;
- off = (addr - vma->vm_start) >> PAGE_SHIFT;
- if (pfn == vma->vm_pgoff + off)
- return NULL;
- if (!is_cow_mapping(vma->vm_flags))
- return NULL;
- }
}
-
- if (is_huge_zero_pfn(pfn))
- return NULL;
-
- /*
- * NOTE! We still have PageReserved() pages in the page tables.
- * eg. VDSO mappings can cause them to exist.
- */
-out:
- VM_WARN_ON_ONCE(!pfn_valid(pfn));
- return pfn_to_page(pfn);
+ return vm_normal_page_pfn(vma, addr, pfn);
}
struct folio *vm_normal_folio_pmd(struct vm_area_struct *vma,
--
2.49.0
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