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Re: [vfio-users] Cannot register eventfd with MSI/MSI-X interrupts




 
> Date: Tue, 2 Aug 2016 16:29:52 -0600
> From: alex williamson redhat com
> To: the_cartographer hotmail com
> CC: vfio-users redhat com
> Subject: Re: [vfio-users] Cannot register eventfd with MSI/MSI-X interrupts
>
> On Tue, 2 Aug 2016 09:54:19 -0600
> Alex Williamson <alex williamson redhat com> wrote:
>
> > On Tue, 2 Aug 2016 10:21:30 +0000
> > chris thompson <the_cartographer hotmail com> wrote:
> >
> > > Hi Alex,
> > >
> > > Thanks for your patience, I noticed the count != 0 issue shortly after, but I get the same EINVAL error anyway when it is zero - but this is because the IRQ does not have a mapping yet. When I change the code to map it then unmap it then I get:
> > > IRQx - successful map then unmap
> > > MSI - unsuccessful map (and unsuccessful unmap)
> > > MSIX - successful map then unmap (despite the device still being in IRQx mode?)
> > > Error - successfully map, kernel driver crash on the unmap!
>
> I remembered that there is a trick here specific to MSI, your device
> probably supports more than one MSI vector. MSI is a little bit
> special, not all platforms support multiple MSI vectors and they were
> pretty much outdated by the much more flexible MSI-X capability for
> that reason. To help with this the SET_IRQS ioctl returns negative on
> error, 0 on success, and a positive value indicating the available
> vectors to retry with if the requested count is not supported/available.
>
> BTW, this should fix the oops you found:
> https://lkml.org/lkml/2016/8/2/1912
>
> Thanks,
> Alex
 
Hi Alex,
 
Indeed I realise now that the MSI registration ioctl returns 8, the number of IRQs I would expect (the same as the MSIX ones). The question is, why doesn't the IRQ_INFO ioctl reply count = 8 like the MSIX one? Instead it returns 64 (I thought MSI only went up to 32 too?)
 
config IRQ index 1
Info:
argsz 0x10, flags 0x9, index 0x1, count 0x40,
Register:
failed to register interrupt set 1 : 0-63, error 8 Invalid argument
 
config IRQ index 2
Info:
argsz 0x10, flags 0x9, index 0x2, count 0x8,
Register:
successfully registered interrupt set 2 : 0-7, ret 0
 
Thanks,
Chris

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