linux-kernel - Re: [PATCH 4.19 043/190] KVM: hyperv: define VP assist page helpers

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Date:   Sun, 15 Sep 2019 16:19:43 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Ladi Prosek <lprosek@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Liran Alon <liran.alon@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 4.19 043/190] KVM: hyperv: define VP assist page helpers

On Sun, Sep 15, 2019 at 09:01:30PM +0200, Pavel Machek wrote:
>On Fri 2019-09-13 14:04:58, Greg Kroah-Hartman wrote:
>> [ Upstream commit 72bbf9358c3676bd89dc4bd8fb0b1f2a11c288fc ]
>>
>> The state related to the VP assist page is still managed by the LAPIC
>> code in the pv_eoi field.
>
>I don't get it.
>
>>
>> +bool kvm_hv_assist_page_enabled(struct kvm_vcpu *vcpu)
>> +{
>> +	if (!(vcpu->arch.hyperv.hv_vapic & HV_X64_MSR_VP_ASSIST_PAGE_ENABLE))
>> +		return false;
>> +	return vcpu->arch.pv_eoi.msr_val & KVM_MSR_ENABLED;
>> +}
>> +EXPORT_SYMBOL_GPL(kvm_hv_assist_page_enabled);
>> +
>> +bool kvm_hv_get_assist_page(struct kvm_vcpu *vcpu,
>> +			    struct hv_vp_assist_page *assist_page)
>> +{
>> +	if (!kvm_hv_assist_page_enabled(vcpu))
>> +		return false;
>> +	return !kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.pv_eoi.data,
>> +				      assist_page, sizeof(*assist_page));
>> +}
>> +EXPORT_SYMBOL_GPL(kvm_hv_get_assist_page);
>> +
>
>This adds two functions, but not their users. What bug is it fixing? I
>don't see any users in the next patch, either.

Look closer at the following patch.

--
Thanks,
Sasha