From: Radim Krčmář <rkrcmar@redhat.com>
Date: Wed, 29 Nov 2017 21:23:41 +0000 (+0100)
Subject: KVM: x86: prevent MWAIT in guest with buggy MONITOR
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=2a140f3b6e23a309453b6f68709a50ece543f0f4;p=linux.git

KVM: x86: prevent MWAIT in guest with buggy MONITOR

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 <agraf@suse.de>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---

diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index d0b95b7a90b4e..81f5f50794f66 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