linux-kernel - Re: [PATCH] kvm: clear kvmclock MSR on reset

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Message-ID: <87wod439hq.fsf@vitty.brq.redhat.com>
Date:   Wed, 16 Oct 2019 19:06:57 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     suleiman@...gle.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH] kvm: clear kvmclock MSR on reset

Paolo Bonzini <pbonzini@...hat.com> writes:

> After resetting the vCPU, the kvmclock MSR keeps the previous value but it is
> not enabled.  This can be confusing, so fix it.
>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/x86.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f26f8be4e621..a55252c69118 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2533,6 +2533,7 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
>  static void kvmclock_reset(struct kvm_vcpu *vcpu)
>  {
>  	vcpu->arch.pv_time_enabled = false;
> +	vcpu->arch.time = 0;
>  }
>  
>  static void kvm_vcpu_flush_tlb(struct kvm_vcpu *vcpu, bool invalidate_gpa)
> @@ -2698,8 +2699,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	case MSR_KVM_SYSTEM_TIME: {
>  		struct kvm_arch *ka = &vcpu->kvm->arch;
>  
> -		kvmclock_reset(vcpu);
> -
>  		if (vcpu->vcpu_id == 0 && !msr_info->host_initiated) {
>  			bool tmp = (msr == MSR_KVM_SYSTEM_TIME);
>  
> @@ -2713,14 +2712,13 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
>  
>  		/* we verify if the enable bit is set... */
> +		vcpu->arch.pv_time_enabled = false;
>  		if (!(data & 1))
>  			break;
>  
>  		if (kvm_gfn_to_hva_cache_init(vcpu->kvm,
>  		     &vcpu->arch.pv_time, data & ~1ULL,
>  		     sizeof(struct pvclock_vcpu_time_info)))
> -			vcpu->arch.pv_time_enabled = false;
> -		else
>  			vcpu->arch.pv_time_enabled = true;

Hm, are you sure you didn't want to write !kvm_gfn_to_hva_cache_init()?

>  
>  		break;

-- 
Vitaly