Re: [PATCH MANUALSEL 5.14 6/9] KVM: x86: nVMX: don't fail nested VM entry on invalid guest state if !from_vmentry

[Paolo Bonzini]

On 06/10/21 15:30, Sasha Levin wrote:
> From: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
>
> [ Upstream commit c8607e4a086fae05efe5bffb47c5199c65e7216e ]
>
> It is possible that when non root mode is entered via special entry
> (!from_vmentry), that is from SMM or from loading the nested state,
> the L2 state could be invalid in regard to non unrestricted guest mode,
> but later it can become valid.
>
> (for example when RSM emulation restores segment registers from SMRAM)
>
> Thus delay the check to VM entry, where we will check this and fail.
>
> Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> Message-Id: <20210913140954.165665-7-mlevitsk@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>   arch/x86/kvm/vmx/nested.c | 7 ++++++-
>   arch/x86/kvm/vmx/vmx.c    | 5 ++++-
>   2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index ac1803dac435..2e8a46f9f552 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2576,8 +2576,13 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
>   	 * Guest state is invalid and unrestricted guest is disabled,
>   	 * which means L1 attempted VMEntry to L2 with invalid state.
>   	 * Fail the VMEntry.
> +	 *
> +	 * However when force loading the guest state (SMM exit or
> +	 * loading nested state after migration, it is possible to
> +	 * have invalid guest state now, which will be later fixed by
> +	 * restoring L2 register state
>   	 */
> -	if (CC(!vmx_guest_state_valid(vcpu))) {
> +	if (CC(from_vmentry && !vmx_guest_state_valid(vcpu))) {
>   		*entry_failure_code = ENTRY_FAIL_DEFAULT;
>   		return -EINVAL;
>   	}
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 339116ff236f..974029917713 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6613,7 +6613,10 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
>   	 * consistency check VM-Exit due to invalid guest state and bail.
>   	 */
>   	if (unlikely(vmx->emulation_required)) {
> -		vmx->fail = 0;
> +
> +		/* We don't emulate invalid state of a nested guest */
> +		vmx->fail = is_guest_mode(vcpu);
> +
>   		vmx->exit_reason.full = EXIT_REASON_INVALID_STATE;
>   		vmx->exit_reason.failed_vmentry = 1;
>   		kvm_register_mark_available(vcpu, VCPU_EXREG_EXIT_INFO_1);

NACK (depends on patch 5)