[PATCH] arm64: KVM: Only skip MMIO insn once

[Andrew Jones <drjones@redhat.com>]

If after an MMIO exit to userspace a VCPU is immediately run with an
immediate_exit request, such as when a signal is delivered or an MMIO
emulation completion is needed, then the VCPU completes the MMIO
emulation and immediately returns to userspace. As the exit_reason
does not get changed from KVM_EXIT_MMIO in these cases we have to
be careful not to complete the MMIO emulation again, when the VCPU is
eventually run again, because the emulation does an instruction skip
(and doing too many skips would be a waste of guest code :-) We need
to use additional VCPU state to track if the emulation is complete.
As luck would have it, we already have 'mmio_needed', which even
appears to be used in this way by other architectures already.

Fixes: 0d640732dbeb ("arm64: KVM: Skip MMIO insn after emulation")
Signed-off-by: Andrew Jones <drjones@redhat.com>
---
 virt/kvm/arm/arm.c  | 3 ++-
 virt/kvm/arm/mmio.c | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index 35a069815baf..322cf9030bbe 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -669,7 +669,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 	if (ret)
 		return ret;
 
-	if (run->exit_reason == KVM_EXIT_MMIO) {
+	if (vcpu->mmio_needed) {
+		vcpu->mmio_needed = 0;
 		ret = kvm_handle_mmio_return(vcpu, vcpu->run);
 		if (ret)
 			return ret;
diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
index a8a6a0c883f1..2d9b5e064ae0 100644
--- a/virt/kvm/arm/mmio.c
+++ b/virt/kvm/arm/mmio.c
@@ -201,6 +201,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	if (is_write)
 		memcpy(run->mmio.data, data_buf, len);
 	vcpu->stat.mmio_exit_user++;
+	vcpu->mmio_needed	= 1;
 	run->exit_reason	= KVM_EXIT_MMIO;
 	return 0;
 }
-- 
2.18.1