On Tue, Dec 4, 2018 at 11:27 AM Krish Sadhukhan
<krish.sadhukhan@xxxxxxxxxx> wrote:
>
> According to section "VM-entry Failures During or After Loading Guest State"
> in Intel SDM vol 3C,
>
> "No MSRs are saved into the VM-exit MSR-store area."
>
> when bit 31 of the exit reason is set.
>
> Reported-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>
> Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>
> Reviewed-by: Darren Kenny <darren.kenny@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx.c | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 4555077..9e1a640 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -13827,6 +13827,19 @@ static void prepare_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
> * L2 to IDT_VECTORING_INFO_FIELD.
> */
> vmcs12_save_pending_event(vcpu, vmcs12);
> +
> + /*
> + * There's no need to store the guest's MSRs if we exit
> + * due to a VM-entry failure that occurs during or after
> + * loading the guest state, because the guest has not
> + * executed any instruction in that case. However, here we
> + * are past that point. So we need to save the MSRs.
> + */
Executing instructions is a distraction. The specification indicates
that these MSRs are stored even in cases where no guest instruction
has executed, so long as the VM-exit was not due to a VM-entry failure
during or after loading guest state. There's no need to store the
guest's MSRs if the exit was due to a VM-entry failure during or after
loading guest state (and, in fact, it is incorrect to do so), because
the specification indicates that these MSRs are not stored in that
case.
> + if (nested_vmx_store_msr(vcpu,
> + vmcs12->vm_exit_msr_store_addr,
> + vmcs12->vm_exit_msr_store_count))
> + nested_vmx_abort(vcpu,
> + VMX_ABORT_SAVE_GUEST_MSR_FAIL);
> }
>
> /*
> @@ -14159,10 +14172,6 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
> * immutable.
> */
> nested_flush_cached_shadow_vmcs12(vcpu, vmcs12);
> -
> - if (nested_vmx_store_msr(vcpu, vmcs12->vm_exit_msr_store_addr,
> - vmcs12->vm_exit_msr_store_count))
> - nested_vmx_abort(vcpu, VMX_ABORT_SAVE_GUEST_MSR_FAIL);
> } else {
> /*
> * The only expected VM-instruction error is "VM entry with
> --
> 2.9.5
>
