[PATCH 2/4] KVM: x86: prevent MWAIT in guest with buggy MONITOR

From: "Radim Krčmář" <rkrcmar@redhat.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Alexander Graf <agraf@suse.de>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"Gabriel L. Somlo" <gsomlo@gmail.com>
Subject: [PATCH 2/4] KVM: x86: prevent MWAIT in guest with buggy MONITOR
Date: Wed,  3 May 2017 21:37:31 +0200	[thread overview]
Message-ID: <20170503193733.13409-3-rkrcmar@redhat.com> (raw)
In-Reply-To: <20170503193733.13409-1-rkrcmar@redhat.com>

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.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 arch/x86/kvm/x86.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 3ed7dd8737ab..63d5fb65ea30 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -231,6 +231,9 @@ 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
-- 
2.12.2
