[v1,2/2] i386: do kvm_put_msr_feature_control() first thing when vCPU is reset

Commit Message

Vitaly Kuznetsov Aug. 18, 2022, 3:01 p.m. UTC

kvm_put_sregs2() fails to reset 'locked' CR4/CR0 bits upon vCPU reset when
it is in VMX root operation. Do kvm_put_msr_feature_control() before
kvm_put_sregs2() to (possibly) kick vCPU out of VMX root operation. It also
seems logical to do kvm_put_msr_feature_control() before
kvm_put_nested_state() and not after it, especially when 'real' nested
state is set.

Signed-off-by: Vitaly Kuznetsov <[e-mail]>
---
 target/i386/kvm/kvm.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

Patch

diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 4f8dacc1d4b5..a1fd1f53791d 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -4529,6 +4529,18 @@  int kvm_arch_put_registers(CPUState *cpu, int level)
 
     assert(cpu_is_stopped(cpu) || qemu_cpu_is_self(cpu));
 
+    /*
+     * Put MSR_IA32_FEATURE_CONTROL first, this ensures the VM gets out of VMX
+     * root operation upon vCPU reset. kvm_put_msr_feature_control() should also
+     * preceed kvm_put_nested_state() when 'real' nested state is set.
+     */
+    if (level >= KVM_PUT_RESET_STATE) {
+        ret = kvm_put_msr_feature_control(x86_cpu);
+        if (ret < 0) {
+            return ret;
+        }
+    }
+
     /* must be before kvm_put_nested_state so that EFER.SVME is set */
     ret = has_sregs2 ? kvm_put_sregs2(x86_cpu) : kvm_put_sregs(x86_cpu);
     if (ret < 0) {
@@ -4540,11 +4552,6 @@  int kvm_arch_put_registers(CPUState *cpu, int level)
         if (ret < 0) {
             return ret;
         }
-
-        ret = kvm_put_msr_feature_control(x86_cpu);
-        if (ret < 0) {
-            return ret;
-        }
     }
 
     if (level == KVM_PUT_FULL_STATE) {