[PATCH 4.4 162/162] hugetlbfs: flush TLBs correctly after huge_pmd_unshare

Greg Kroah-Hartman
2021-11-24T12:12:07Z

From: Nadav Amit <namit@vmware.com>

commit a4a118f2eead1d6c49e00765de89878288d4b890 upstream.

When __unmap_hugepage_range() calls to huge_pmd_unshare() succeed, a TLB
flush is missing. This TLB flush must be performed before releasing the
i_mmap_rwsem, in order to prevent an unshared PMDs page from being
released and reused before the TLB flush took place.

Arguably, a comprehensive solution would use mmu_gather interface to
batch the TLB flushes and the PMDs page release, however it is not an
easy solution: (1) try_to_unmap_one() and try_to_migrate_one() also call
huge_pmd_unshare() and they cannot use the mmu_gather interface; and (2)
deferring the release of the page reference for the PMDs page until
after i_mmap_rwsem is dropeed can confuse huge_pmd_unshare() into
thinking PMDs are shared when they are not.

Fix __unmap_hugepage_range() by adding the missing TLB flush, and
forcing a flush when unshare is successful.

Fixes: 24669e58477e ("hugetlb: use mmu_gather instead of a temporary linked list for accumulating pages)" # 3.6
Signed-off-by: Nadav Amit <namit@vmware.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/asm-generic/tlb.h | 7 +++++++
mm/hugetlb.c | 5 ++++-
2 files changed, 11 insertions(+), 1 deletion(-)

--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -165,6 +165,13 @@ static inline void __tlb_reset_range(str
#define tlb_end_vma __tlb_end_vma
#endif

+static inline void tlb_flush_pmd_range(struct mmu_gather *tlb,
+ unsigned long address, unsigned long size)
+{
+ tlb->start = min(tlb->start, address);
+ tlb->end = max(tlb->end, address + size);
+}
+
#ifndef __tlb_remove_tlb_entry
#define __tlb_remove_tlb_entry(tlb, ptep, address) do { } while (0)
#endif
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3290,8 +3290,11 @@ again:
continue;

ptl = huge_pte_lock(h, mm, ptep);
- if (huge_pmd_unshare(mm, &address, ptep))
+ if (huge_pmd_unshare(mm, &address, ptep)) {
+ tlb_flush_pmd_range(tlb, address & PUD_MASK, PUD_SIZE);
+ force_flush = 1;
goto unlock;
+ }

pte = huge_ptep_get(ptep);
if (huge_pte_none(pte))