Commit 8e9b29b6 authored Apr 11, 2018 by KarimAllah Ahmed Committed by Paolo Bonzini Apr 11, 2018

X86/KVM: Do not allow DISABLE_EXITS_MWAIT when LAPIC ARAT is not available



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 <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Reported-by: Wanpeng Li <kernellwp@gmail.com>
Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 4d5f26ee

arch/x86/kvm/x86.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -2819,7 +2819,8 @@ out:
		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)

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