linux-kernel - [PATCH 17/18] Indicate reliable TSC in kvmclock

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Message-Id: <1278986892-11733-18-git-send-email-zamsden@redhat.com>
Date:	Mon, 12 Jul 2010 16:08:11 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	KVM <kvm@...r.kernel.org>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Glauber Costa <glommer@...hat.com>
Cc:	Linux-kernel <linux-kernel@...r.kernel.org>,
	Zachary Amsden <zamsden@...hat.com>
Subject: [PATCH 17/18] Indicate reliable TSC in kvmclock

When no platform bugs have been detected, no TSC warps have been
detected, and the hardware guarantees to us TSC does not change
rate or stop with P-state or C-state changes, we can consider it reliable.

Signed-off-by: Zachary Amsden <zamsden@...hat.com>
---
 arch/x86/kvm/x86.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c55cdf9..d110c84 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -55,6 +55,7 @@
 #include <asm/mce.h>
 #include <asm/i387.h>
 #include <asm/xcr.h>
+#include <asm/pvclock-abi.h>
 
 #define MAX_IO_MSRS 256
 #define CR0_RESERVED_BITS						\
@@ -902,6 +903,13 @@ static inline int kvm_tsc_changes_freq(void)
 	return ret;
 }
 
+static inline int kvm_tsc_reliable(void)
+{
+	return (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
+		boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
+		!check_tsc_unstable());
+}
+
 static inline u64 nsec_to_cycles(u64 nsec)
 {
 	WARN_ON(preemptible());
@@ -1024,7 +1032,7 @@ static int kvm_write_guest_time(struct kvm_vcpu *v)
 	vcpu->hv_clock.tsc_timestamp = tsc_timestamp;
 	vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset;
 	vcpu->last_kernel_ns = kernel_ns;
-	vcpu->hv_clock.flags = 0;
+	vcpu->hv_clock.flags = kvm_tsc_reliable() ? PVCLOCK_TSC_STABLE_BIT : 0;
 
 	/*
 	 * The interface expects us to write an even number signaling that the
-- 
1.7.1

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