On Fri, 2022-01-14 at 10:58 +0800, Chao Gao wrote:
> On Thu, Jan 13, 2022 at 10:19:21PM +0000, Sean Christopherson wrote:
> > On Tue, Jan 11, 2022, Maxim Levitsky wrote:
> > > Both Intel and AMD's PRM also state that changing APIC ID is implementation
> > > dependent.
> > >  
> > > I vote to forbid changing apic id, at least in the case any APIC acceleration
> > > is used, be that APICv or AVIC.
> > 
> > That has my vote as well.  For IPIv in particular there's not much concern with
> > backwards compability, i.e. we can tie the behavior to enable_ipiv.
Great!
> 
> Hi Sean and Levitsky,
> 
> Let's align on the implementation.
> 
> To disable changes for xAPIC ID when IPIv/AVIC is enabled:
> 
> 1. introduce a variable (forbid_apicid_change) for this behavior in kvm.ko
> and export it so that kvm-intel, kvm-amd can set it when IPIv/AVIC is
> enabled. To reduce complexity, this variable is a module level setting.
> 
> 2. when guest attempts to change xAPIC ID but it is forbidden, KVM prints
> a warning on host and injects a #GP to guest.
> 
> 3. remove AVIC code that deals with changes to xAPIC ID.
> 

I have a patch for both, I attached them.
I haven't tested either of these patches that much other than a smoke test,
but I did test all of the guests I  have and none broke in regard to boot.

I will send those patches as part of larger patch series that implements
nesting for AVIC. I hope to do this next week.

Best regards,
	Maxim Levitsky