Re: [RFC kvm-unit-tests PATCH 2/4] x86/apic: Disable PIT for x2apic test to allow SVM AVIC to be tested

[Sean Christopherson <seanjc@google.com>]

On Tue, Feb 25, 2025, Naveen N Rao (AMD) wrote:
> SVM AVIC is inhibited if kvm-pit is enabled in the default "reinject"
> mode. Commit f5cfdd33cb21 ("x86/apic: Add test config to allow running
> apic tests against SVM's AVIC") disabled PIT in xapic test to allow AVIC
> to be tested. However, since then, AVIC has been enabled to work in
> x2apic mode, but still requires PIT to either be disabled or set to
> "discard".
> 
> Update x2apic test to disable PIT so that AVIC can be exercized with
> x2apic.
> 
> Signed-off-by: Naveen N Rao (AMD) <naveen@kernel.org>
> ---
>  x86/unittests.cfg | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/x86/unittests.cfg b/x86/unittests.cfg
> index 8d046e6d7356..35fb88c3cb79 100644
> --- a/x86/unittests.cfg
> +++ b/x86/unittests.cfg
> @@ -14,10 +14,11 @@ extra_params = -cpu qemu64,+x2apic,+tsc-deadline -machine kernel_irqchip=split
>  arch = x86_64
>  groups = apic
>  
> +# Don't create a Programmable Interval Timer (PIT, a.k.a 8254) to allow testing SVM's AVIC
>  [x2apic]
>  file = apic.flat
>  smp = 2
> -extra_params = -cpu qemu64,+x2apic,+tsc-deadline
> +extra_params = -cpu qemu64,+x2apic,+tsc-deadline -machine pit=off

Similar to the split IRQ chip, playing whack-a-mole to disable the PIT in every
test where (x2)AVIC might be interesting is rather silly.  The realmode test
uses the PIT, but AFAICT it doesn't need re-injection, i.e. we can simply disable
re-injection mode to get the same effect, e.g.

    qemu-429929  [233] ...1. 16531.028284: kvm_apicv_inhibit_changed: set reason=9, inhibits=0x200 PIT_REINJ
    qemu-429929  [233] ...1. 16531.028311: kvm_apicv_inhibit_changed: cleared reason=9, inhibits=0x0

I'll send a patch.

>  arch = x86_64
>  timeout = 30
>  groups = apic
> -- 
> 2.48.1
>