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

[chris thompson]

> Date: Tue, 2 Aug 2016 16:29:52 -0600
> From: alex.williamson at redhat.com
> To: the_cartographer at hotmail.com
> CC: vfio-users at 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 at redhat.com> wrote:
> 
> > On Tue, 2 Aug 2016 10:21:30 +0000
> > chris thompson <the_cartographer at 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 pretty much outdated by the much more flexible MSI-X capability for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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