[v2,1/3] KVM: x86: prevent MWAIT in guest with buggy MONITOR

Commit Message

Radim Krčmář Nov. 29, 2017, 9:23 p.m. UTC

The bug prevents MWAIT from waking up after a write to the monitored
cache line.
KVM might emulate a CPU model that shouldn't have the bug, so the guest
would not employ a workaround and possibly miss wakeups.
Better to avoid the situation.

Reviewed-by: Alexander Graf <[e-mail]>
Signed-off-by: Radim Krčmář <[e-mail]>
---
 arch/x86/kvm/x86.h | 3 +++
 1 file changed, 3 insertions(+)

Patch

diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index d0b95b7a90b4..81f5f50794f6 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -281,6 +281,9 @@  static inline bool kvm_mwait_in_guest(void)
 		return false;
 	}
 
+	if (boot_cpu_has_bug(X86_BUG_MONITOR))
+		return false;
+
 	/*
 	 * Intel CPUs without CPUID5_ECX_INTERRUPT_BREAK are problematic as
 	 * they would allow guest to stop the CPU completely by disabling