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

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Date:   Tue, 3 Nov 2020 08:43:51 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
CC:     "Jiang, Dave" <dave.jiang@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "Dey, Megha" <megha.dey@...el.com>,
        "maz@...nel.org" <maz@...nel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Lu, Baolu" <baolu.lu@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "jing.lin@...el.com" <jing.lin@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "netanelg@...lanox.com" <netanelg@...lanox.com>,
        "shahafs@...lanox.com" <shahafs@...lanox.com>,
        "yan.y.zhao@...ux.intel.com" <yan.y.zhao@...ux.intel.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Ortiz, Samuel" <samuel.ortiz@...el.com>,
        "Hossain, Mona" <mona.hossain@...el.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection

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.

Jason