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

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Date:	Tue, 26 May 2015 09:22:40 -0400
From:	Luiz Capitulino <lcapitulino@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	Owen Hofmann <osh@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>,
	KVM General <kvm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [PATCH v2] KVM: x86: zero kvmclock_offset when vcpu0
 initializes kvmclock system MSR

On Sat, 23 May 2015 17:06:29 -0300
Marcelo Tosatti <mtosatti@...hat.com> wrote:

> 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>

Tested-by: Luiz Capitulino <lcapitulino@...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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