linux-kernel - [PATCH v2] KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmclock system MSR

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Message-ID: <20150523200629.GA18207@amt.cnet>
Date:	Sat, 23 May 2015 17:06:29 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Owen Hofmann <osh@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc:	KVM General <kvm@...r.kernel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: [PATCH v2] KVM: x86: zero kvmclock_offset when vcpu0 initializes
 kvmclock system MSR

Initialize kvmclock base, on kvmclock system MSR write time, 
so that the guest sees kvmclock counting from zero.

This matches baremetal behaviour when kvmclock in guest
sets sched clock stable.

Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cc2c759..ea40d24 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2188,6 +2188,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 					&vcpu->requests);
 
 			ka->boot_vcpu_runs_old_kvmclock = tmp;
+
+			ka->kvmclock_offset = -get_kernel_ns();
 		}
 
 		vcpu->arch.time = data;
--
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