linux-kernel - [PATCH] kvm: svm: move WARN_ON in svm_adjust_tsc

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Date:	Wed, 12 Nov 2014 21:00:39 -0600
From:	Chris J Arges <chris.j.arges@...onical.com>
To:	kvm@...r.kernel.org
Cc:	Chris J Arges <chris.j.arges@...onical.com>,
	Joerg Roedel <joro@...tes.org>, Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] kvm: svm: move WARN_ON in svm_adjust_tsc_offset

When running the tsc_adjust kvm-unit-test on an AMD processor with the
IA32_TSC_ADJUST feature enabled, the WARN_ON in svm_adjust_tsc_offset can be
triggered. This WARN_ON checks for a negative adjustment in case __scale_tsc
is called; however it may trigger unnecessary warnings.

This patch moves the WARN_ON to trigger only if __scale_tsc will actually be
called from svm_adjust_tsc_offset. In addition make adj in kvm_set_msr_common
s64 since this can have signed values.

Signed-off-by: Chris J Arges <chris.j.arges@...onical.com>
---
 arch/x86/kvm/svm.c | 8 +++++---
 arch/x86/kvm/x86.c | 2 +-
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index d4f3aaa..6b411ad 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1056,9 +1056,11 @@ static void svm_adjust_tsc_offset(struct kvm_vcpu *vcpu, s64 adjustment, bool ho
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
-	WARN_ON(adjustment < 0);
-	if (host)
-		adjustment = svm_scale_tsc(vcpu, adjustment);
+	if (host) {
+		if (svm->tsc_ratio != TSC_RATIO_DEFAULT)
+			WARN_ON(adjustment < 0);
+		adjustment = svm_scale_tsc(vcpu, (u64)adjustment);
+	}
 
 	svm->vmcb->control.tsc_offset += adjustment;
 	if (is_guest_mode(vcpu))
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f85da5c..1cd1376 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2141,7 +2141,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_IA32_TSC_ADJUST:
 		if (guest_cpuid_has_tsc_adjust(vcpu)) {
 			if (!msr_info->host_initiated) {
-				u64 adj = data - vcpu->arch.ia32_tsc_adjust_msr;
+				s64 adj = data - vcpu->arch.ia32_tsc_adjust_msr;
 				kvm_x86_ops->adjust_tsc_offset(vcpu, adj, true);
 			}
 			vcpu->arch.ia32_tsc_adjust_msr = data;
-- 
1.9.1

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