Re: [PATCH v2 4/7] KVM: nVMX: Force enlightened VMCS sync from nested_vmx_failValid()

Maxim Levitsky
2021-05-24T12:28:02Z

On Mon, 2021-05-17 at 15:50 +0200, Vitaly Kuznetsov wrote:
> 'need_vmcs12_to_shadow_sync' is used for both shadow and enlightened
> VMCS sync when we exit to L1. The comment in nested_vmx_failValid()
> validly states why shadow vmcs sync can be omitted but this doesn't
> apply to enlightened VMCS as it 'shadows' all VMCS12 fields.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> arch/x86/kvm/vmx/nested.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index ec476f64df73..eb2d25a93356 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -194,9 +194,13 @@ static int nested_vmx_failValid(struct kvm_vcpu *vcpu,
> | X86_EFLAGS_ZF);
> get_vmcs12(vcpu)->vm_instruction_error = vm_instruction_error;
> /*
> - * We don't need to force a shadow sync because
> - * VM_INSTRUCTION_ERROR is not shadowed
> + * We don't need to force sync to shadow VMCS because
> + * VM_INSTRUCTION_ERROR is not shadowed. Enlightened VMCS 'shadows' all
> + * fields and thus must be synced.
> */
> + if (nested_evmcs_is_used(to_vmx(vcpu)))
> + to_vmx(vcpu)->nested.need_vmcs12_to_shadow_sync = true;

Cool, this is a bug that I noticed too while reviewing
previous patches in this series.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
Maxim Levitsky

> +
> return kvm_skip_emulated_instruction(vcpu);
> }
>