KVM: s390/mm: Fix CMMA reset during reboot

commit 1e133ab296f ("s390/mm: split arch/s390/mm/pgtable.c") factored
out the page table handling code from __gmap_zap and  __s390_reset_cmma
into ptep_zap_unused and added a simple flag that tells which one of the
function (reset or not) is to be made. This also changed the behaviour,
as it also zaps unused page table entries on reset.
Turns out that this is wrong as s390_reset_cmma uses the page walker,
which DOES NOT take the ptl lock.

The most simple fix is to not do the zapping part on reset (which uses
the walker)

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Fixes: 1e133ab296f ("s390/mm: split arch/s390/mm/pgtable.c")
Cc: stable@vger.kernel.org # 4.6+
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 4324b87f93982f08552ecb86bb9c893431507427..9f0ce0e6eeb484c2fad96f560a3b5ca851188ea8 100644 (file)
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -437,7 +437,7 @@ void ptep_zap_unused(struct mm_struct *mm, unsigned long addr,
        pgste = pgste_get_lock(ptep);
        pgstev = pgste_val(pgste);
        pte = *ptep;
-       if (pte_swap(pte) &&
+       if (!reset && pte_swap(pte) &&
            ((pgstev & _PGSTE_GPS_USAGE_MASK) == _PGSTE_GPS_USAGE_UNUSED ||
             (pgstev & _PGSTE_GPS_ZERO))) {
                ptep_zap_swap_entry(mm, pte_to_swp_entry(pte));