Re: [Xen-devel] [PATCH v2 2/2] x86/HVM: fix ID handling of x2APIC emulation

[Tim Deegan <tim@xxxxxxx>]

At 08:57 +0100 on 12 Sep (1410508628), Jan Beulich wrote:
> >> @@ -1254,6 +1255,29 @@ HVM_REGISTER_SAVE_RESTORE(LAPIC, lapic_s
> >>  HVM_REGISTER_SAVE_RESTORE(LAPIC_REGS, lapic_save_regs, lapic_load_regs,
> >>                            1, HVMSR_PER_VCPU);
> >>  
> >> +void vlapic_domain_unpause(const struct domain *d)
> >> +{
> >> +    /*
> >> +     * Following lapic_load_hidden()/lapic_load_regs() we may need to
> >> +     * correct ID and LDR when they come from an old, broken hypervisor.
> >> +     */
> > 
> > This seems like aweful overhead for the domain_{,un}pause() path.
> 
> It's the best I could think of (and domain un-pausing shouldn't be that
> frequent an operation I would hope), since ...
> 
> >  Why can't it be fixed up once in lapic_load_{regs,hidden}(),
> 
> ... both of these would have to have got carried out and ...

You're already tracking whether either of them happens so you could
track whether both have happened and do the fixup then.  Loading a VM
with only the hidden state and not the register state is not something
we care about (and in that case, by construction, LDR won't be 1).

Tim.

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