Re: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection

[Jason Gunthorpe]

On Wed, Nov 04, 2020 at 03:41:33AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Sent: Tuesday, November 3, 2020 8:44 PM
> > 
> > On Tue, Nov 03, 2020 at 02:49:27AM +0000, Tian, Kevin wrote:
> > 
> > > > There is a missing hypercall to allow the guest to do this on its own,
> > > > presumably it will someday be fixed so IMS can work in guests.
> > >
> > > Hypercall is VMM specific, while IMS cap provides a VMM-agnostic
> > > interface so any guest driver (if following the spec) can seamlessly
> > > work on all hypervisors.
> > 
> > It is a *VMM* issue, not PCI. Adding a PCI cap to describe a VMM issue
> > is architecturally wrong.
> > 
> > IMS *can not work* in any hypervsior without some special
> > hypercall. Just block it in the platform code and forget about the PCI
> > cap.
> > 
> 
> It's per-device thing instead of platform thing. If the VMM understands
> the IMS format of a specific device and virtualize it to the guest,

Please no! Adding device specific emulation is just going down deeper
into this bad architecture.

Interrupts is a platform issue. Using emulation of MSI to dynamically
insert vectors to a VM was a reasonable, but hacky thing. Now it needs
proper platform support.

Jason