Re: [Xen-devel] [PATCH v5 1/3] xen/pt: fix some pass-thru devices don't work across reboot

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.01.19 at 06:50, <chao.gao@xxxxxxxxx> wrote:
> On Wed, Jan 16, 2019 at 11:38:23AM +0100, Roger Pau Monné wrote:
>>On Wed, Jan 16, 2019 at 04:17:30PM +0800, Chao Gao wrote:
>>> @@ -1529,6 +1591,8 @@ int deassign_device(struct domain *d, u16 seg, u8 
>>> bus, u8 devfn)
>>>      if ( !pdev )
>>>          return -ENODEV;
>>>  
>>> +    pci_unmap_msi(pdev);
>>
>>Just want to make sure, since deassign_device will be called for both
>>PV and HVM domains. AFAICT pci_unmap_msi is safe to call when the
>>device is assigned to a PV guest, but would like your confirmation.
> 
> Tested with a PV guest loaded by Pygrub. PV guest doesn't suffer the
> msi-x issue I want to fix.
> 
> With these three patches applied, I got some error messages from Xen
> and Dom0 as follow:
> 
> (XEN) irq.c:2176: dom3: forcing unbind of pirq 332
> (XEN) irq.c:2176: dom3: forcing unbind of pirq 331
> (XEN) irq.c:2176: dom3: forcing unbind of pirq 328
> (XEN) irq.c:2148: dom3: pirq 359 not mapped
> [ 2887.067685] xen:events: unmap irq failed -22
> (XEN) irq.c:2148: dom3: pirq 358 not mapped
> [ 2887.075917] xen:events: unmap irq failed -22
> (XEN) irq.c:2148: dom3: pirq 357 not mapped
> 
> It seems, the cause of such error is that pirq-s are unmapped and forcibly
> unbound on deassignment; subsequent unmapping pirq issued by dom0 fail.
> From some aspects, this error is expected. Because with this patch,
> pirq-s are expected to be mapped by qemu or dom0 kernel (for pv case) before
> deassignment and mapping/binding pirq after deassignment should fail.
> 
> So what's your opinion on handling such error? We should figure out another
> method to fix msi-x issue to avoid such error or suppress these errors in
> qemu and linux kernel?

The "forcing unbind" ones are probably fine to leave alone, but
the errors would better be avoided in Xen (i.e. without a need
to also change qemu and/or Linux). Since you don't really say
when / why these errors now surface, it's hard to suggest what
might be best to do.

Jan


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