[PATCH v1 5/8] KVM: s390: Fix race in __do_essa()

[Claudio Imbrenda]

An unlikely race between __do_essa() and kvm_s390_vm_start_migration(),
kvm_s390_vm_stop_migration(), or dat_get_cmma() was possible.

Fix by locking kvm->slots_lock. Since this is not a hot path, the
overhead of an additional mutex is negligible.

Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
---
 arch/s390/kvm/priv.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
index ad0ddc433a73..b0f3a47b1829 100644
--- a/arch/s390/kvm/priv.c
+++ b/arch/s390/kvm/priv.c
@@ -1260,8 +1260,9 @@ static int handle_essa(struct kvm_vcpu *vcpu)
 		/* Retry the ESSA instruction */
 		kvm_s390_retry_instr(vcpu);
 	} else {
-		scoped_guard(read_lock, &vcpu->kvm->mmu_lock)
-			i = __do_essa(vcpu, orc);
+		scoped_guard(mutex, &vcpu->kvm->slots_lock)
+			scoped_guard(read_lock, &vcpu->kvm->mmu_lock)
+				i = __do_essa(vcpu, orc);
 		if (i < 0)
 			return i;
 		/* Account for the possible extra cbrl entry */
-- 
2.55.0