Re: [PATCH v6 2/3] xen/arm: Enable the existing x86 virtual PCI support for ARM.

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Oct 15, 2021 at 03:00:21PM +0100, Luca Fancellu wrote:
> 
> 
> > On 15 Oct 2021, at 14:47, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
> > 
> > On Fri, Oct 15, 2021 at 10:48:41AM +0000, Bertrand Marquis wrote:
> >> Hi Jan,
> >> 
> >>> On 15 Oct 2021, at 11:41, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> >>> 
> >>> On 15.10.2021 12:33, Bertrand Marquis wrote:
> >>>>> On 15 Oct 2021, at 11:24, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> >>>>> On 15.10.2021 11:52, Bertrand Marquis wrote:
> >>>>>>> On 15 Oct 2021, at 09:32, Roger Pau Monné <roger.pau@xxxxxxxxxx> 
> >>>>>>> wrote:
> >>>>>>> On Thu, Oct 14, 2021 at 03:49:50PM +0100, Bertrand Marquis wrote:
> >>>>>>>> @@ -752,6 +752,19 @@ int pci_add_device(u16 seg, u8 bus, u8 devfn,
> >>>>>>>> 
> >>>>>>>>  check_pdev(pdev);
> >>>>>>>> 
> >>>>>>>> +#ifdef CONFIG_ARM
> >>>>>>>> +    /*
> >>>>>>>> +     * On ARM PCI devices discovery will be done by Dom0. Add vpci 
> >>>>>>>> handler when
> >>>>>>>> +     * Dom0 inform XEN to add the PCI devices in XEN.
> >>>>>>>> +     */
> >>>>>>>> +    ret = vpci_add_handlers(pdev);
> >>>>>>>> +    if ( ret )
> >>>>>>>> +    {
> >>>>>>>> +        printk(XENLOG_ERR "Setup of vPCI failed: %d\n", ret);
> >>>>>>>> +        goto out;
> >>>>>>>> +    }
> >>>>>>>> +#endif
> >>>>>>> 
> >>>>>>> I think vpci_add_handlers should be called after checking that
> >>>>>>> pdev->domain is != NULL, so I would move this chunk a bit below.
> >>>>>> 
> >>>>>> On arm this would prevent the dom0less use case or to have the PCI
> >>>>>> bus enumerated from an other domain.
> >>>>>> @oleksandr: can you comment on this one, you might have a better
> >>>>>> answer than me on this ?
> >>>>> 
> >>>>> Well, without Xen doing the enumeration, some other entity would need
> >>>>> to do so, including the reporting to Xen. Obviously without a Dom0 it
> >>>>> would be ambiguous which domain to assign the device to; perhaps it
> >>>>> should be the caller in this case? That would make that caller domain
> >>>>> a pseudo-hwdom though, as far as PCI is concerned, which may not be
> >>>>> desirable according to my (limited) understanding of dom0less.
> >>>> 
> >>>> This is not really related to this patch but the plan is the following:
> >>>> - enumeration would have to be done by the firmware or boot loader before
> >>>> - xen will have some code to detect PCI devices
> >>>> - dom0less can be used to assign PCI devices to guest
> >>>> 
> >>>> Anyway does not change the fact that this must be called when domain is
> >>>> not NULL and I will fix that.
> >>> 
> >>> Since we now all seem to agree that the NULL would have been a problem,
> >>> may I ask in how far any of this has actually been tested?
> >> 
> >> With the whole serie currently on gitlab we have extensively tested passing
> >> through PCI devices on Arm in several configuration (number of device, MSI,
> >> MSI-X) and check that PCI was still functional on x86.
> >> 
> >> With the patches pushed to Xen right now it was checked that:
> >> - xen compiles properly on arm32, arm64 and x86
> >> - xen compiles properly with VPCI activated (using a patch) on arm32 and 
> >> arm64
> >> - xen on x86 is functionnal (using basic test on QEMU)
> >> - xen on arm64 is functionnal (with some extensive tests on different 
> >> targets)
> > 
> > I thinks it's unlikely, but since I haven't checked myself, could you
> > see if the vpci user-space test harness (tools/tests/vpci) still
> > builds and functions properly?
> 
> Hi Roger,
> 
> Bertrand is going to send the v7, however I’m keen to do this test but 
> unfortunately
> I’ve never used it before and I don’t have an x86 environment, do you have any
> resource that I can read or some guidance?

Oh, you just need to build it (make) and then run it (make run). If
it returns success everything is fine.

Regards, Roger.