[PATCH v1 09/14] mm/mshare: Do not free PTEs for mshare'd PTEs

Khalid Aziz
2022-04-11T16:09:14Z

mshare'd PTEs should not be removed when a task exits. These PTEs
are removed when the last task sharing the PTEs exits. Add a check
for shared PTEs and skip them.

Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
---
mm/memory.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index c77c0d643ea8..e7c5bc6f8836 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -419,16 +419,25 @@ void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *vma,
} else {
/*
* Optimization: gather nearby vmas into one call down
+ * as long as they all belong to the same mm (that
+ * may not be the case if a vma is part of mshare'd
+ * range
*/
while (next && next->vm_start <= vma->vm_end + PMD_SIZE
- && !is_vm_hugetlb_page(next)) {
+ && !is_vm_hugetlb_page(next)
+ && vma->vm_mm == tlb->mm) {
vma = next;
next = vma->vm_next;
unlink_anon_vmas(vma);
unlink_file_vma(vma);
}
- free_pgd_range(tlb, addr, vma->vm_end,
- floor, next ? next->vm_start : ceiling);
+ /*
+ * Free pgd only if pgd is not allocated for an
+ * mshare'd range
+ */
+ if (vma->vm_mm == tlb->mm)
+ free_pgd_range(tlb, addr, vma->vm_end,
+ floor, next ? next->vm_start : ceiling);
}
vma = next;
}
@@ -1551,6 +1560,13 @@ void unmap_page_range(struct mmu_gather *tlb,
pgd_t *pgd;
unsigned long next;

+ /*
+ * If this is an mshare'd page, do not unmap it since it might
+ * still be in use.
+ */
+ if (vma->vm_mm != tlb->mm)
+ return;
+
BUG_ON(addr >= end);
tlb_start_vma(tlb, vma);
pgd = pgd_offset(vma->vm_mm, addr);
--
2.32.0