Re: [PATCH v2] kvm: Disable MSI/MSI-X in assigned device reset path

[Avi Kivity <avi@redhat.com>]

On 04/08/2012 06:46 PM, Michael S. Tsirkin wrote:
> > > > 
> > > > I'm thinking about this flow:
> > > > 
> > > >   FLR the device
> > > >   for each emulated register
> > > >      read it from the hardware
> > > >      if different from emulated register:
> > > >         update the internal model (for example, disabling MSI in kvm if
> > > > needed)
> > >
> > > If we do it this way we get back the problem this patch
> > > is trying to solve: MSIX assigned while device
> > > memory is disabled would cause unsupported request errors.
> > 
> > Why is that?  FLR would presumably disable MSI in the device, and this
> > line would disable it in kvm as well.
>
> The bug is that device memory is disabled (FLR would do that)
> while MSI is enabled in kvm. The fix is to
> disable MSI in kvm first.

Yes, no need to repeat.  My question is whether my pseudo-code does the
same and whether or not if it is better (when applied to all emulated
config space).

> > > Doing this in kernel seems more robust, otherwise
> > > we risk losing the device if qemu gets killed
> > > before it has restored the registers.
> > 
> > Doesn't the driver have to enable MSIX if it attaches to the device at
> > that point, anyway?
>
> Yes. I'm talking about things like enabling memory, setting up irq register,
> etc though. Most of this setup is done by bios.

I see.  So should we have a pci_reset_function() variant that limits
itself to restoring just those bits?



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