Marking PMDs that map a "normal" refcounted folios as special is
against our rules documented for vm_normal_page().
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 just inlining the relevant code, making the whole
pmd_none() handling cleaner. We can now use folio_mk_pmd().
While at it, make sure that a pmd that is not-none is actually present
before comparing PFNs.
Fixes: 6c88f72691f8 ("mm/huge_memory: add vmf_insert_folio_pmd()")
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
mm/huge_memory.c | 39 ++++++++++++++++++++++++++++++++-------
1 file changed, 32 insertions(+), 7 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d3e66136e41a3..f9e23dfea76f8 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1474,9 +1474,10 @@ 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;
+ pmd_t *pmd = vmf->pmd;
spinlock_t *ptl;
pgtable_t pgtable = NULL;
- int error;
+ pmd_t entry;
if (addr < vma->vm_start || addr >= vma->vm_end)
return VM_FAULT_SIGBUS;
@@ -1490,17 +1491,41 @@ vm_fault_t vmf_insert_folio_pmd(struct vm_fault *vmf,
struct folio *folio,
return VM_FAULT_OOM;
}
- ptl = pmd_lock(mm, vmf->pmd);
- if (pmd_none(*vmf->pmd)) {
+ ptl = pmd_lock(mm, pmd);
+ if (pmd_none(*pmd)) {
folio_get(folio);
folio_add_file_rmap_pmd(folio, &folio->page, vma);
add_mm_counter(mm, mm_counter_file(folio), HPAGE_PMD_NR);
+
+ entry = folio_mk_pmd(folio, vma->vm_page_prot);
+ if (write) {
+ entry = pmd_mkyoung(pmd_mkdirty(entry));
+ entry = maybe_pmd_mkwrite(entry, vma);
+ }
+ set_pmd_at(mm, addr, pmd, entry);
+ update_mmu_cache_pmd(vma, addr, pmd);
+
+ if (pgtable) {
+ pgtable_trans_huge_deposit(mm, pmd, pgtable);
+ mm_inc_nr_ptes(mm);
+ pgtable = NULL;
+ }
+ } else if (pmd_present(*pmd) && write) {
+ /*
+ * We only allow for upgrading write permissions if the
+ * same folio is already mapped.
+ */
+ if (pmd_pfn(*pmd) == folio_pfn(folio)) {
+ entry = pmd_mkyoung(*pmd);
+ entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+ if (pmdp_set_access_flags(vma, addr, pmd, entry, 1))
+ update_mmu_cache_pmd(vma, addr, pmd);
+ } else {
+ WARN_ON_ONCE(!is_huge_zero_pmd(*pmd));
+ }
}
- error = insert_pfn_pmd(vma, addr, vmf->pmd,
- pfn_to_pfn_t(folio_pfn(folio)), vma->vm_page_prot,
- write, pgtable);
spin_unlock(ptl);
- if (error && pgtable)
+ if (pgtable)
pte_free(mm, pgtable);
return VM_FAULT_NOPAGE;
--
2.49.0
