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

[Avi Kivity <avi@redhat.com>]

On 04/08/2012 07:04 PM, Michael S. Tsirkin wrote:
> On Sun, Apr 08, 2012 at 06:50:27PM +0300, Avi Kivity wrote:
> > 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
>
> It doesn't seem to: FLR (disabling memory) is followed
> by MSI disable in kvm instead of the reverse.

Ah, so the problem is the ordering?  I see.

> > and whether or not if it is better (when applied to all emulated
> > config space).
>
> I'm not sure.
> I would like to see an example of a register that you have
> in mind.

I went over the PCI registers and saw none that would be affected.

> > >
> > > 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?
>
> We only need kernel to restore whatever qemu emulates, but
> kernel doesn't know what that is.
> What kind of interface do you have in mind?
>

The same as pci_reset_function(), but leaves MSI clear.

I guess it's not worth it if the ordering problem is there.

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