On Wed, 2018-04-11 at 11:16 +0200, KarimAllah Ahmed wrote:
> If the processor does not have an "Always Running APIC Timer" (aka ARAT),
> we should not give guests direct access to MWAIT. The LAPIC timer would
> stop ticking in deep C-states, so any host deadlines would not wakeup the
> host kernel.
>
> The host kernel intel_idle driver handles this by switching to broadcast
> mode when ARAT is not available and MWAIT is issued with a deep C-state
> that would stop the LAPIC timer. When MWAIT is passed through, we can not
> tell when MWAIT is issued.
>
> So just disable this capability when LAPIC ARAT is not available. I am not
> even sure if there are any CPUs with VMX support but no LAPIC ARAT or not.
ARAT was added on WSM, so NHM, the Core 2 family and a few PSC SKUs
support VMX+MWAIT but not ARAT.
> Cc: Paolo Bonzini
> Cc: Radim Krčmář
> Cc: Thomas Gleixner
> Cc: Ingo Molnar
> Cc: H. Peter Anvin
> Cc: x...@kernel.org
> Cc: k...@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Reported-by: Wanpeng Li
> Signed-off-by: KarimAllah Ahmed
> ---
> arch/x86/kvm/x86.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b2ff74b..0334b25 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2819,7 +2819,8 @@ static int msr_io(struct kvm_vcpu *vcpu, struct
> kvm_msrs __user *user_msrs,
> static inline bool kvm_can_mwait_in_guest(void)
> {
> return boot_cpu_has(X86_FEATURE_MWAIT) &&
> - !boot_cpu_has_bug(X86_BUG_MONITOR);
> + !boot_cpu_has_bug(X86_BUG_MONITOR) &&
> + boot_cpu_has(X86_FEATURE_ARAT);
> }
>
> int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
