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Re: [Qemu-devel] [Xen-devel] [PATCH 5/6] xen-pt: Hide MSI-X from xen stu
From: |
Jason Andryuk |
Subject: |
Re: [Qemu-devel] [Xen-devel] [PATCH 5/6] xen-pt: Hide MSI-X from xen stubdoms |
Date: |
Tue, 12 Mar 2019 09:58:56 -0400 |
On Tue, Mar 12, 2019 at 8:38 AM Marek Marczykowski-Górecki
<address@hidden> wrote:
>
> On Tue, Mar 12, 2019 at 01:04:19PM +0100, Roger Pau Monné wrote:
> > On Mon, Mar 11, 2019 at 02:02:15PM -0400, Jason Andryuk wrote:
> > > MSI-X is not supported in Xen stubdoms, so it must be disabled. Use the
> > > existing xen_pt_hide_dev_cap to hide when running under -xen-stubdom.
> >
> > I'm afraid this requires some more context. What's the actual issue
> > that prevents MSI-X from working?
>
> At least missing "Fix PCI passthrough for HVM with stubdomain" series,
> but that's mostly on Xen side (+ one change how QEMU enable MSI-X in
> config space).
> Some of it can be worked around by enabling permissive mode. Jason, did
> you had a chance to test it with any MSI-X device?
> I'm not aware of anything thing particular that breaks MSI-X but not
> MSI. Besides much less devices lying around to test MSI-X...
OpenXT and Qubes have used a compile time patch that disabled MSI-X
for a long time. The OpenXT patch description doesn't help:
"""
Currently we do not support MSI-X setup for PCI devices passed through.
Although the specification mentions that PCI-e devices might implement only
MSI-X there is not a lot of those and mostly none that we have encountered yet.
Considering that, we force devices to use MSI by hiding the MSI-X capability.
"""
To be honest, I didn't question the reasoning and just made the
compile-time disabling into a runtime disabling.
I tested with a NEC uPD720200 XHCI controller supporting MSI-X. There
was an error related to setting up MSI-X when I failed to pass the
"-xen-stubdom" flag. I can pull that log when I get back to the
machine. With this patch, MSI-X was hidden in the guest, but dom0
showed MSI-X present but unused.
Marek, is "Use xc_physdev_msi_set_enable for enabling MSI..." the QEMU
patch you are refer to? Do you think permissive mode would allow
MSI-X to work without that patch? I could test that out.
Regards,
Jason
[Qemu-devel] [PATCH 4/6] xen: Set HVM_PARAM_DM_DOMAIN for stubdom on older Xen, Jason Andryuk, 2019/03/11
[Qemu-devel] [PATCH 2/6] xen: Move xenstore initialization to common location, Jason Andryuk, 2019/03/11
[Qemu-devel] [PATCH 6/6] xen-pt: Round pci regions sizes to XEN_PAGE_SIZE, Jason Andryuk, 2019/03/11