Messages in this thread | | | Subject | Re: [PATCH] X86/KVM: Do not allow DISABLE_EXITS_MWAIT when LAPIC ARAT is not available | From | Sean Christopherson <> | Date | Wed, 11 Apr 2018 07:02:49 -0700 |
| |
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 <pbonzini@redhat.com> > Cc: Radim Krčmář <rkrcmar@redhat.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: H. Peter Anvin <hpa@zytor.com> > Cc: x86@kernel.org > Cc: kvm@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Reported-by: Wanpeng Li <kernellwp@gmail.com> > Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de> > --- > 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)
| |