linux-kernel - Re: [PATCH v4 5/5] x86, kvm: support vcpu preempted check

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Message-ID: <1a556fcf-e071-8c32-7a4b-ca7a2ffc17e9@redhat.com>
Date:   Mon, 24 Oct 2016 17:18:36 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org,
        linux-s390@...r.kernel.org, xen-devel-request@...ts.xenproject.org,
        kvm@...r.kernel.org, benh@...nel.crashing.org, paulus@...ba.org,
        mpe@...erman.id.au, mingo@...hat.com, peterz@...radead.org,
        paulmck@...ux.vnet.ibm.com, will.deacon@....com,
        kernellwp@...il.com, jgross@...e.com, bsingharora@...il.com,
        boqun.feng@...il.com, borntraeger@...ibm.com
Subject: Re: [PATCH v4 5/5] x86, kvm: support vcpu preempted check



On 24/10/2016 17:14, Radim Krčmář wrote:
> 2016-10-24 16:39+0200, Paolo Bonzini:
>> On 19/10/2016 19:24, Radim Krčmář wrote:
>>>>> +	if (vcpu->arch.st.msr_val & KVM_MSR_ENABLED)
>>>>> +		if (kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
>>>>> +					&vcpu->arch.st.steal,
>>>>> +					sizeof(struct kvm_steal_time)) == 0) {
>>>>> +			vcpu->arch.st.steal.preempted = 1;
>>>>> +			kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
>>>>> +					&vcpu->arch.st.steal,
>>>>> +					sizeof(struct kvm_steal_time));
>>>>> +		}
>>> Please name this block of code.  Something like
>>>   kvm_steal_time_set_preempted(vcpu);
>>
>> While at it:
>>
>> 1) the kvm_read_guest_cached is not necessary.  You can rig the call to
>> kvm_write_guest_cached so that it only writes vcpu->arch.st.steal.preempted.
> 
> I agree.  kvm_write_guest_cached() always writes from offset 0, so we'd
> want a new function that allows to specify a starting offset.

Yeah, let's leave it for a follow-up then!

Thanks,

Paolo

> Using cached vcpu->arch.st.steal to avoid the read wouldn't be as good.
>