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

[Avi Kivity <avi@redhat.com>]

On 04/08/2012 04:53 PM, Michael S. Tsirkin wrote:
> On Sun, Apr 08, 2012 at 04:41:27PM +0300, Avi Kivity wrote:
> > On 04/08/2012 04:30 PM, Michael S. Tsirkin wrote:
> > > On Sun, Apr 08, 2012 at 04:24:11PM +0300, Avi Kivity wrote:
> > > > On 04/08/2012 04:21 PM, Michael S. Tsirkin wrote:
> > > > > On Sun, Apr 08, 2012 at 04:18:29PM +0300, Avi Kivity wrote:
> > > > > > On 04/08/2012 04:17 PM, Michael S. Tsirkin wrote:
> > > > > > > > 
> > > > > > > > Don't we FLR the device, which ought to disable MSI on the real device?
> > > > > > >
> > > > > > > AFAIK we call pci_reset, which saves device state, does an FLR
> > > > > > > and then restores the state. I think this might include msi as well.
> > > > > > >
> > > > > > >
> > > > > > 
> > > > > > Then that is wrong as well, no?
> > > > >
> > > > > Not as such assuming we disable msi/msix first :)
> > > > 
> > > > I think we need to fix both, no?
> > >
> > > Isn't this what this patch does?
> > 
> > If we change pci_reset() (or a variant that we call) to reset MSI, and
> > update qemu to synchronize from the device after pci_reset(), then we
> > achieve the same result, in a different way.
>
> MSI vectors are set up by kvm in the host. So we should not
> abruptly drop that by a sysfs write: would need to
> synchronise with kvm. Once we do, there's nothing left
> for pci_reset to do.

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)
        set emulated register to hardware value

> > Since reset can change other config space registers, we achieve
> > correctness for more of them.
>
> Which other registers do you have in mind?

BARs for example.  We may have our own reset for this, but isn't copying
the hardware values more trustworthy?

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