Re: [PATCH-for-9.0 v2 06/19] hw/pci/msi: Restrict xen_is_pirq_msi() call to Xen

[Philippe Mathieu-Daudé]

On 14/11/23 16:13, David Woodhouse wrote:
> On 14 November 2023 09:38:02 GMT-05:00, "Philippe Mathieu-Daudé" 
> <philmd@linaro.org> wrote:
> > Similarly to the restriction in hw/pci/msix.c (see commit
> > e1e4bf2252 "msix: fix msix_vector_masked"), restrict the
> > xen_is_pirq_msi() call in msi_is_masked() to Xen.
> >
> > Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>
> Hm, we do also support the Xen abomination of snooping on MSI table writes to 
> see if they're targeted at a Xen PIRQ, then actually unmasking the MSI from 
> QEMU when the guest binds the corresponding event channel to that PIRQ.
>
> I think this is going to break in CI as kvm_xen_guest.py does deliberately 
> exercise that use case, doesn't it?

Hmmm I see what you mean.

So you mentioned these checks:

- host Xen accel
- Xen accel emulated to guest via KVM host accel

Maybe we need here:

- guest expected to run Xen

  Being (
                Xen accel emulated to guest via KVM host accel
        OR
                host Xen accel
        )

If so, possibly few places incorrectly check 'xen_enabled()'
instead of this 'xen_guest()'.

"Xen on KVM" is a tricky case...

> I deliberately *didn't* switch to testing the Xen PV net device, with a comment 
> that testing MSI and irqchip permutations was far more entertaining. So I hope 
> it should catch this?

¯\_(ツ)_/¯