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

Tian, Kevin
2020-11-04T13:34:21Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Wednesday, November 4, 2020 8:40 PM
>
> On Wed, Nov 04, 2020 at 03:41:33AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > 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

Interrupt controller is a platform issue. Interrupt source is about device.

> insert vectors to a VM was a reasonable, but hacky thing. Now it needs
> proper platform support.
>

why is MSI emulation a hacky thing? isn't it defined by PCISIG? I guess
that I must misunderstand your real point here...

Thanks
Kevin