KVM: nVMX: Reset eVMCS clean fields data from prepare_vmcs02()

When nested state migration happens during L1's execution, it
is incorrect to modify eVMCS as it is L1 who 'owns' it at the moment.
At least genuine Hyper-V seems to not be very happy when 'clean fields'
data changes underneath it.

'Clean fields' data is used in KVM twice: by copy_enlightened_to_vmcs12()
and prepare_vmcs02_rare() so we can reset it from prepare_vmcs02() instead.

While at it, update a comment stating why exactly we need to reset
'hv_clean_fields' data from L0.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210526132026.270394-10-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index c73668b..2bdc9a2 100644 (file)
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2059,14 +2059,10 @@ void nested_sync_vmcs12_to_shadow(struct kvm_vcpu *vcpu)
 {
        struct vcpu_vmx *vmx = to_vmx(vcpu);
 
-       if (evmptr_is_valid(vmx->nested.hv_evmcs_vmptr)) {
+       if (evmptr_is_valid(vmx->nested.hv_evmcs_vmptr))
                copy_vmcs12_to_enlightened(vmx);
-               /* All fields are clean */
-               vmx->nested.hv_evmcs->hv_clean_fields |=
-                       HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL;
-       } else {
+       else
                copy_vmcs12_to_shadow(vmx);
-       }
 
        vmx->nested.need_vmcs12_to_shadow_sync = false;
 }
@@ -2616,6 +2612,17 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
 
        kvm_rsp_write(vcpu, vmcs12->guest_rsp);
        kvm_rip_write(vcpu, vmcs12->guest_rip);
+
+       /*
+        * It was observed that genuine Hyper-V running in L1 doesn't reset
+        * 'hv_clean_fields' by itself, it only sets the corresponding dirty
+        * bits when it changes a field in eVMCS. Mark all fields as clean
+        * here.
+        */
+       if (evmptr_is_valid(vmx->nested.hv_evmcs_vmptr))
+               vmx->nested.hv_evmcs->hv_clean_fields |=
+                       HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL;
+
        return 0;
 }