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mm/huge_memory: don't mark refcounted folios special in vmf_insert_folio_pmd()

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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.

Link: https://lkml.kernel.org/r/20250613092702.1943533-3-david@redhat.com
Fixes: 6c88f72691 ("mm/huge_memory: add vmf_insert_folio_pmd()")
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2025-06-13 11:27:01 +02:00 committed by Andrew Morton
parent 09fefdca80
commit c4297465d4
1 changed files with 40 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

59
mm/huge_memory.c
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@ -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);