A few checks were missing in gmap_helper_zap_one_page(), which can lead to memory corruption in the guest under specific circumstances. Add the missing checks. Fixes: 5deafa27d9ae ("KVM: s390: Fix to clear PTE when discarding a swapped page") Reported-by: Marc Hartmayer Signed-off-by: Claudio Imbrenda --- arch/s390/mm/gmap_helpers.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/s390/mm/gmap_helpers.c b/arch/s390/mm/gmap_helpers.c index d4c3c36855e2..38a2d82cd88a 100644 --- a/arch/s390/mm/gmap_helpers.c +++ b/arch/s390/mm/gmap_helpers.c @@ -47,6 +47,7 @@ static void ptep_zap_swap_entry(struct mm_struct *mm, swp_entry_t entry) void gmap_helper_zap_one_page(struct mm_struct *mm, unsigned long vmaddr) { struct vm_area_struct *vma; + unsigned long pgstev; spinlock_t *ptl; pgste_t pgste; pte_t *ptep; @@ -65,9 +66,13 @@ void gmap_helper_zap_one_page(struct mm_struct *mm, unsigned long vmaddr) if (pte_swap(*ptep)) { preempt_disable(); pgste = pgste_get_lock(ptep); + pgstev = pgste_val(pgste); - ptep_zap_swap_entry(mm, pte_to_swp_entry(*ptep)); - pte_clear(mm, vmaddr, ptep); + if ((pgstev & _PGSTE_GPS_USAGE_MASK) == _PGSTE_GPS_USAGE_UNUSED || + (pgstev & _PGSTE_GPS_ZERO)) { + ptep_zap_swap_entry(mm, pte_to_swp_entry(*ptep)); + pte_clear(mm, vmaddr, ptep); + } pgste_set_unlock(ptep, pgste); preempt_enable(); -- 2.51.1