On Tue, Aug 13, 2019 at 04:13:03PM +0300, Nikita Leshenko wrote:
> Fail VM entry if GUEST_ACTIVITY_HLT is unsupported. According to "SDM A.6 -
> Miscellaneous Data", VM entry should fail if the HLT activity is not marked as
> supported on IA32_VMX_MISC MSR.
>
> Usermode might disable GUEST_ACTIVITY_HLT support in the vCPU with
> vmx_restore_vmx_misc(). Before this commit VM entries would have succeeded
> anyway.
Is there a use case for disabling GUEST_ACTIVITY_HLT? Or can we simply
disallow writes to IA32_VMX_MISC that disable GUEST_ACTIVITY_HLT?
To disable GUEST_ACTIVITY_HLT, userspace also has to make
CPU_BASED_HLT_EXITING a "must be 1" control, otherwise KVM will be
presenting a bogus model to L1.
The bad model is visible to L1 if CPU_BASED_HLT_EXITING is set by L0,
i.e. KVM is running without kvm_hlt_in_guest(), and cleared by L1. In
that case, a HLT from L2 will be handled in L0. L0 will set the state to
KVM_MP_STATE_HALTED and report to L1 (on a nested VM-Exit, e.g. INTR),
that the activity state is GUEST_ACTIVITY_HLT, which from L1's perspective
doesn't exist.
> Reviewed-by: Liran Alon <liran.alon@xxxxxxxxxx>
> Reviewed-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
> Signed-off-by: Nikita Leshenko <nikita.leshchenko@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx/nested.c | 16 ++++++++++++----
> arch/x86/kvm/vmx/nested.h | 5 +++++
> 2 files changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 46af3a5e9209..3165e2f7992f 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2656,11 +2656,19 @@ static int nested_vmx_check_vmcs_link_ptr(struct kvm_vcpu *vcpu,
> /*
> * Checks related to Guest Non-register State
> */
> -static int nested_check_guest_non_reg_state(struct vmcs12 *vmcs12)
> +static int nested_check_guest_non_reg_state(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
> {
> - if (vmcs12->guest_activity_state != GUEST_ACTIVITY_ACTIVE &&
> - vmcs12->guest_activity_state != GUEST_ACTIVITY_HLT)
> + switch (vmcs12->guest_activity_state) {
> + case GUEST_ACTIVITY_ACTIVE:
> + /* Always supported */
> + break;
> + case GUEST_ACTIVITY_HLT:
> + if (!nested_cpu_has_activity_state_hlt(vcpu))
> + return -EINVAL;
> + break;
> + default:
> return -EINVAL;
> + }
>
> return 0;
> }
> @@ -2710,7 +2718,7 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
> (vmcs12->guest_bndcfgs & MSR_IA32_BNDCFGS_RSVD)))
> return -EINVAL;
>
> - if (nested_check_guest_non_reg_state(vmcs12))
> + if (nested_check_guest_non_reg_state(vcpu, vmcs12))
> return -EINVAL;
>
> return 0;
> diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
> index e847ff1019a2..4a294d3ff820 100644
> --- a/arch/x86/kvm/vmx/nested.h
> +++ b/arch/x86/kvm/vmx/nested.h
> @@ -123,6 +123,11 @@ static inline bool nested_cpu_has_zero_length_injection(struct kvm_vcpu *vcpu)
> return to_vmx(vcpu)->nested.msrs.misc_low & VMX_MISC_ZERO_LEN_INS;
> }
>
> +static inline bool nested_cpu_has_activity_state_hlt(struct kvm_vcpu *vcpu)
> +{
> + return to_vmx(vcpu)->nested.msrs.misc_low & VMX_MISC_ACTIVITY_HLT;
> +}
> +
> static inline bool nested_cpu_supports_monitor_trap_flag(struct kvm_vcpu *vcpu)
> {
> return to_vmx(vcpu)->nested.msrs.procbased_ctls_high &
> --
> 2.20.1
>
