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    SubjectRe: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection
    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
    insert vectors to a VM was a reasonable, but hacky thing. Now it needs
    proper platform support.

    Jason

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