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Date: Mon, 24 Oct 2016 17:14:18 +0200
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>, linux-kernel@vger.kernel.org,
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Subject: Re: [PATCH v4 5/5] x86, kvm: support vcpu preempted check
Message-ID: <20161024151417.GC2247@potion>
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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.

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