On Mon, Jan 21, 2013 at 11:34:20PM +0200, Gleb Natapov wrote:
> On Mon, Jan 21, 2013 at 07:21:13PM -0200, Marcelo Tosatti wrote:
> > On Mon, Jan 21, 2013 at 10:21:14PM +0200, Gleb Natapov wrote:
> > > > > }
> > > > > +
> > > > > + vcpu->arch.apic_base = value;
> > > >
> > > > Simpler to have
> > > >
> > > > if (apic_x2apic_mode(apic)) {
> > > > ...
> > > > kvm_x86_ops->set_virtual_x2apic_mode(vcpu, true);
> > > > } else {
> > > > kvm_x86_ops->set_virtual_x2apic_mode(vcpu, false);
> > > > }
> > > >
> > > This will not work during cpu init. That was discussed on one of
> > > the previous iterations of the patch. When this code is called during
> > > vcpu init vmcs is not loaded yet so set_virtual_x2apic_mode() cannot
> > > write into it.
> >
> > Are you saying that the logic to write on bit value change is due to
> > ordering with cpu init or that the callback is at the wrong place?
> >
> The logic is because of ordering with cpu init.
OK. Still must move this conditional callback after assignment of apic_base.
> > > > Why not disable write intercept for all MSRs which represent APIC registers
> > > > that are virtualized? Why TPR is special?
> > > >
> > > This patch goes before vid is enabled. At this point only TPR is
> > > vitalized. If APIC_WRITE exit will be generated on unhandled MSR write
> > > then we can disable intercept for all x2apic MSRs here.
> >
> > -ENOPARSE, please be more verbose. "unhandled MSR write" ?
> By unhandled I mean unintercepted. Write to x2apic MSR will either
> generate MSR write exit if msr bitmap says so and then x2apic MSR will
> be handled just like today, or, if we disable intercept, it will
> generate APIC_WRITE exit (need to consult SDM here, not sure about it).
> One is not really preferable to the other.
It will generate APIC_WRITE, for example, if due to EOI virtualization
exiting.
The question is, why is intercept for EOI MSR address (0x80B) not being
disabled here, while TPR is? I don't see intercept disabled by other
patches either.
APIC_WRITE exit (conditional, see EOI virtualization page) is
preferable to MSR write exit (unconditional).
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