linux-kernel - [PATCH v2] KVM: x86: Prevent exposing TSC deadline timer feature in the absence of in-kernel APIC

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Date:	Wed, 21 Dec 2011 11:25:39 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alexey Zaytsev <alexey.zaytsev@...il.com>,
	"Liu, Jinsong" <jinsong.liu@...el.com>, Avi Kivity <avi@...hat.com>
CC:	Kernel development list <linux-kernel@...r.kernel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	"Garrett D'Amore" <garrett@...enta.com>, kvm <kvm@...r.kernel.org>
Subject: [PATCH v2] KVM: x86: Prevent exposing TSC deadline timer feature
 in the absence of in-kernel APIC

We must not report the TSC deadline timer feature on our own when user
space provides the APIC as we have no clue about its features.

Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
---

Changes in v2:
 - reorganized code to make the flow clearer

 arch/x86/kvm/cpuid.c |   18 ++++++++----------
 1 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 230f713..b7cdd3b 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -27,7 +27,6 @@ void kvm_update_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct kvm_cpuid_entry2 *best;
 	struct kvm_lapic *apic = vcpu->arch.apic;
-	u32 timer_mode_mask;
 
 	best = kvm_find_cpuid_entry(vcpu, 1, 0);
 	if (!best)
@@ -40,15 +39,14 @@ void kvm_update_cpuid(struct kvm_vcpu *vcpu)
 			best->ecx |= bit(X86_FEATURE_OSXSAVE);
 	}
 
-	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
-		best->function == 0x1) {
-		best->ecx |= bit(X86_FEATURE_TSC_DEADLINE_TIMER);
-		timer_mode_mask = 3 << 17;
-	} else
-		timer_mode_mask = 1 << 17;
-
-	if (apic)
-		apic->lapic_timer.timer_mode_mask = timer_mode_mask;
+	if (apic) {
+		if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
+		    best->function == 0x1) {
+			best->ecx |= bit(X86_FEATURE_TSC_DEADLINE_TIMER);
+			apic->lapic_timer.timer_mode_mask = 3 << 17;
+		} else
+			apic->lapic_timer.timer_mode_mask = 1 << 17;
+	}
 
 	kvm_pmu_cpuid_update(vcpu);
 }
-- 
1.7.3.4
--
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