Re: [RFC PATCH] xen/dm: arm: Introudce arm_inject_msi DM op

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 19/12/2023 14:17, Jan Beulich wrote:
> On 19.12.2023 15:12, Julien Grall wrote:
> > On 19/12/2023 13:57, Jan Beulich wrote:
> > > On 19.12.2023 14:48, Mykyta Poturai wrote:
> > > > This patch adds the ability for the device emulator to inject MSI
> > > > interrupts into guests. This is done by adding a new DM op to the device
> > > > model library.
> > > >
> > > > It is not possible to reuse already existing inject_msi DM op, because
> > > > it does not have a devid parameter, which is required for translation of
> > > > MSIs to interrupt numbers on ARM.
> > > Yet then ...
> > >
> > > > @@ -112,6 +113,20 @@ int dm_op(const struct dmop_args *op_args)
> > > >            break;
> > > >        }
> > > >    
> > > > +    case XEN_DMOP_arm_inject_msi:
> > > > +    {
> > > > +        const struct xen_dm_op_arm_inject_msi *data =
> > > > +            &op.u.arm_inject_msi;
> > > > +
> > > > +        if ( d->arch.vgic.its == NULL )
> > > > +        {
> > > > +            rc = -EINVAL;
> > > > +            break;
> > > > +        }
> > > > +        vgic_its_trigger_msi(d, d->arch.vgic.its, data->devid, data->data);
> > > > +        break;
> > > > +
> > > > +    }
> > > ... you're not using the addr field at all, which therefore could likely
> > > hold the devid data (encoded to really represent some form of address,
> > > or stored directly - much depends on what purpose the address serves on
> > > Arm for MSI).
> > For real HW, the address would point to an ITS doorbell. All access will
> > be tagged by the HW with the DeviceID. This is then used with the data
> > (an event ID) to look up the associated interrupt.
> So no properties of the destination are encoded in the address (besides
> it being an ITS specific address of course)?
From my understanding, for the ITS yes. This could be different for 
other MSI controller.
> > I think for Xen on Arm, we want 'addr' to be the SBDF. This could then
> > be used to find the associated vITS and device ID.
> FTAOD, the vSBDF you mean then?
Indeed.

Cheers,

--
Julien Grall