On Sun, 2023-01-15 at 14:12 +0000, David Woodhouse wrote:
> On Wed, 2020-08-26 at 13:16 +0200, Thomas Gleixner wrote:
> > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> >
> > To allow utilizing the irq domain pointer in struct device it is necessary
> > to make XEN/MSI irq domain compatible.
> >
> > While the right solution would be to truly convert XEN to irq domains, this
> > is an exercise which is not possible for mere mortals with limited XENology.
> >
> > Provide a plain irqdomain wrapper around XEN. While this is blatant
> > violation of the irqdomain design, it's the only solution for a XEN igorant
> > person to make progress on the issue which triggered this change.
> >
> > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Acked-by: Juergen Gross <jgross@xxxxxxxx>
>
> I think it broke MSI-X support, because xen_pci_msi_domain_info is
> lacking a .flags = MSI_FLAGS_PCI_MSIX?
Hm, I think it only actually *broke* with commit 99f3d27976 ("PCI/MSI:
Reject MSI-X early") from November last year. So 6.1 was OK and we have
time to fix it in 6.2.
Confirmed on real Xen at least that a Fedora 37 install with a 6.0.7
kernel works fine, then on upgrading to Rawhide's 6.2-rc3 it dies with
[ 41.498694] ena 0000:00:03.0 (unnamed net_device) (uninitialized): Failed to enable MSI-X. irq_cnt -524
[ 41.498705] ena 0000:00:03.0: Can not reserve msix vectors
[ 41.498712] ena 0000:00:03.0: Failed to enable and set the admin interrupts
> > ---
> > Note: This is completely untested, but it compiles so it must be perfect.
>
>
> I'm working on making it simple for you to test that, by hosting Xen
> HVM guests natively in qemu (under KVM¹).
>
> But I'm absolutely not going to try hacking on both guest and host side
> at the same time when I'm trying to ensure compatibility — that way
> lies madness.
>
> So for now I'm going to test qemu with older kernels, and maybe someone
> (Jürgen}? can test MSI-X to PIRQ support under real Xen?) FWIW if I add
> the missing MSI_FLAGS_PCI_MSIX flag then under my qemu I get:
>
> 38: 3180 0 xen-pirq -msi-x ens4-rx-0
> 39: 0 3610 xen-pirq -msi-x ens4-tx-0
> 40: 1 0 xen-pirq -msi-x ens4
>
> But without the flags I get:
>
> [ 8.464212] e1000e 0000:00:04.0 ens4: Failed to initialize MSI interrupts. Falling back to legacy interrupts.
>
> ¹ https://lore.kernel.org/qemu-devel/20230110122042.1562155-1-dwmw2@xxxxxxxxxxxxx/
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