Simplify the shutdown of non-protected VMs. There is no need to do
complex manipulations of the counter if it was zero.
This also fixes a very rare race which caused pages to be torn down
from the address space with a non-zero counter even on older machines
that don't support the UVC instruction, causing a crash.
Reported-by: Marc Hartmayer <mhartmay@xxxxxxxxxxxxx>
Fixes: fb491d5500a7 ("KVM: s390: pv: asynchronous destroy for reboot")
Reviewed-by: Nico Boehr <nrb@xxxxxxxxxxxxx>
Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Message-ID: <20230705111937.33472-2-imbrenda@xxxxxxxxxxxxx>
---
arch/s390/kvm/pv.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
index 2f34c7c3c5ab..bf1fdc7bf89e 100644
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -411,8 +411,12 @@ int kvm_s390_pv_deinit_cleanup_all(struct kvm *kvm, u16 *rc, u16 *rrc)
u16 _rc, _rrc;
int cc = 0;
- /* Make sure the counter does not reach 0 before calling s390_uv_destroy_range */
- atomic_inc(&kvm->mm->context.protected_count);
+ /*
+ * Nothing to do if the counter was already 0. Otherwise make sure
+ * the counter does not reach 0 before calling s390_uv_destroy_range.
+ */
+ if (!atomic_inc_not_zero(&kvm->mm->context.protected_count))
+ return 0;
*rc = 1;
/* If the current VM is protected, destroy it */
--
2.41.0
