linux-kernel - Re: KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmclock system MSR

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Message-ID: <CANqFzA5ByNPnndWzpUo6FuBMyY9sMbrd0q2mRM_JLbao-btuhQ@mail.gmail.com>
Date:	Fri, 22 May 2015 14:40:48 -0700
From:	Owen Hofmann <osh@...gle.com>
To:	Marcelo Tosatti <mtosatti@...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: Re: KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmclock
 system MSR

Change as described sounds good, however:

> @@ -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();
>                 }

Should this be ka->kvmclock_offset = -get_kernel_ns()?
kvm_guest_time_update() sets hv_clock.system_time = kernel_ns +
v->kvm->arch.kvmclock_offset, and similarly kvmclock_offset is added
to the value from get_kernel_ns() in the handler for
HV_X64_MSR_TIME_REF_COUNT.
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