From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Prior to this change DAX PMD mappings that were made read-only were
never able to be made writable again. This is because the code in
insert_pfn_pmd() that calls pmd_mkdirty() and pmd_mkwrite() would skip
these calls if the PMD already existed in the page table.
Instead, if we are doing a write always mark the PMD entry as dirty and
writeable. Without this code we can get into a condition where we mark
the PMD as read-only, and then on a subsequent write fault we get into
an infinite loop of PMD faults where we try unsuccessfully to make the
PMD writeable.
Reported-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
Reported-by: Toshi Kani <toshi.kani@xxxxxxx>
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
mm/huge_memory.c | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index faf39bbf6292..a4bfeb07394b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -967,15 +967,13 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
spinlock_t *ptl;
ptl = pmd_lock(mm, pmd);
- if (pmd_none(*pmd)) {
- entry = pmd_mkhuge(pfn_pmd(pfn, 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);
+ entry = pmd_mkhuge(pfn_pmd(pfn, 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);
spin_unlock(ptl);
}
--
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