From 8e9b29b61851ba452e33373743fadb52778e9075 Mon Sep 17 00:00:00 2001 From: KarimAllah Ahmed Date: Wed, 11 Apr 2018 11:16:03 +0200 Subject: [PATCH] X86/KVM: Do not allow DISABLE_EXITS_MWAIT when LAPIC ARAT is not available MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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. Cc: Paolo Bonzini Cc: Radim Krčmář Reported-by: Wanpeng Li Signed-off-by: KarimAllah Ahmed Signed-off-by: Paolo Bonzini --- 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 b2ff74b12ec4..0334b250e102 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) -- 2.45.2