[PATCH] mm: Fix modifying of page protection by insert_pfn_pmd()

[Aneesh Kumar K.V]

With some architectures like ppc64, set_pmd_at() cannot cope with
a situation where there is already some (different) valid entry present.

Use pmdp_set_access_flags() instead to modify the pfn which is built to
deal with modifying existing PMD entries.

This is similar to
commit cae85cb8add3 ("mm/memory.c: fix modifying of page protection by 
insert_pfn()")

We also do similar update w.r.t insert_pfn_pud eventhough ppc64 don't support
pud pfn entries now.

CC: sta...@vger.kernel.org
Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
---
 mm/huge_memory.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 404acdcd0455..f7dca413c4b2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -755,6 +755,20 @@ 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)) {
+               if (write) {
+                       if (pmd_pfn(*pmd) != pfn_t_to_pfn(pfn)) {
+                               WARN_ON_ONCE(!is_huge_zero_pmd(*pmd));
+                               goto out_unlock;
+                       }
+                       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);
+               }
+               goto out_unlock;
+       }
+
        entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
        if (pfn_t_devmap(pfn))
                entry = pmd_mkdevmap(entry);
@@ -770,6 +784,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, 
unsigned long addr,
 
        set_pmd_at(mm, addr, pmd, entry);
        update_mmu_cache_pmd(vma, addr, pmd);
+out_unlock:
        spin_unlock(ptl);
 }
 
@@ -821,6 +836,20 @@ static void insert_pfn_pud(struct vm_area_struct *vma, 
unsigned long addr,
        spinlock_t *ptl;
 
        ptl = pud_lock(mm, pud);
+       if (!pud_none(*pud)) {
+               if (write) {
+                       if (pud_pfn(*pud) != pfn_t_to_pfn(pfn)) {
+                               WARN_ON_ONCE(!is_huge_zero_pud(*pud));
+                               goto out_unlock;
+                       }
+                       entry = pud_mkyoung(*pud);
+                       entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma);
+                       if (pudp_set_access_flags(vma, addr, pud, entry, 1))
+                               update_mmu_cache_pud(vma, addr, pud);
+               }
+               goto out_unlock;
+       }
+
        entry = pud_mkhuge(pfn_t_pud(pfn, prot));
        if (pfn_t_devmap(pfn))
                entry = pud_mkdevmap(entry);
@@ -830,6 +859,8 @@ static void insert_pfn_pud(struct vm_area_struct *vma, 
unsigned long addr,
        }
        set_pud_at(mm, addr, pud, entry);
        update_mmu_cache_pud(vma, addr, pud);
+
+out_unlock:
        spin_unlock(ptl);
 }
 
-- 
2.20.1