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

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Message-Id: <2f37742f-6839-1ef4-0838-05fb7222f14a@linux.vnet.ibm.com>
Date:   Tue, 25 Oct 2016 09:25:37 +0800
From:   Pan Xinhui <xinhui@...ux.vnet.ibm.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        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



在 2016/10/24 23:18, Paolo Bonzini 写道:
>
>
> 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!
>
I think I can make a having-offset version. :)

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