Re: [PATCH 07/12] libxl: Allow stubdomain to control interupts of PCI device

[Anthony PERARD <anthony.perard@vates.tech>]

On Thu, Jul 25, 2024 at 04:16:37PM +0200, Marek Marczykowski-Górecki wrote:
> On Thu, Jul 25, 2024 at 02:06:04PM +0000, Anthony PERARD wrote:
> > On Thu, May 16, 2024 at 03:58:28PM +0200, Marek Marczykowski-Górecki wrote:
> > > Especially allow it to control MSI/MSI-X enabling bits. This part only
> > > writes a flag to a sysfs, the actual implementation is on the kernel
> > > side.
> > >
> > > This requires Linux >= 5.10 in dom0 (or relevant patch backported).
> >
> > Does it not work before 5.10? Because the
> > Documentation/ABI/testing/sysfs-driver-pciback in linux tree say that
> > allow_interrupt_control is in 5.6.
>
> For MSI-X to work at least with Linux it needs a fixup
> 2c269f42d0f382743ab230308b836ffe5ae9b2ae, which was backported to
> 5.10.201, but not further.
>
> > > diff --git a/tools/libs/light/libxl_pci.c b/tools/libs/light/libxl_pci.c
> > > index 96cb4da0794e..6f357b70b815 100644
> > > --- a/tools/libs/light/libxl_pci.c
> > > +++ b/tools/libs/light/libxl_pci.c
> > > @@ -1513,6 +1513,14 @@ static void pci_add_dm_done(libxl__egc *egc,
> > >              rc = ERROR_FAIL;
> > >              goto out;
> > >          }
> > > +    } else if (libxl_is_stubdom(ctx, domid, NULL)) {
> > > +        /* Allow acces to MSI enable flag in PCI config space for the stubdom */
> >
> > s/acces/access/
> >
> > > +        if ( sysfs_write_bdf(gc, SYSFS_PCIBACK_DRIVER"/allow_interrupt_control",
> > > +                             pci) < 0 ) {
> > > +            LOGD(ERROR, domainid, "Setting allow_interrupt_control for device");
> > > +            rc = ERROR_FAIL;
> > > +            goto out;
> >
> > Is it possible to make this non-fatal for cases where the kernel is
> > older than the introduction of the new setting? Or does pci passthrough
> > doesn't work at all with a stubdom before the change in the kernel?
>
> MSI/MSI-X will not work. And if QEMU wouldn't hide MSI/MSI-X (upstream
> one doesn't), Linux won't fallback to INTx, so the device won't work at
> all.

Ok

I guess this patch is fine then:
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

Thanks,

--

Anthony Perard | Vates XCP-ng Developer

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