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

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Message-ID: <20201112134609.GF2620339@nvidia.com>
Date:   Thu, 12 Nov 2020 09:46:09 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
CC:     "Raj, Ashok" <ashok.raj@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "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>,
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        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...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>,
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Subject: Re: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection

On Wed, Nov 11, 2020 at 02:17:48AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@...dia.com>
> > Sent: Tuesday, November 10, 2020 10:24 PM
> > 
> > On Tue, Nov 10, 2020 at 06:13:23AM -0800, Raj, Ashok wrote:
> > 
> > > This isn't just for idxd, as I mentioned earlier, there are vendors other
> > > than Intel already working on this. In all cases the need for guest direct
> > > manipulation of interrupt store hasn't come up. From the discussion, it
> > > seems like there are devices today or in future that will require direct
> > > manipulation of interrupt store in the guest. This needs additional work
> > > in both the device hardware providing the right plumbing and OS work to
> > > comprehend those.
> > 
> > We'd want to see SRIOV's assigned to guests to be able to use
> > IMS. This allows a SRIOV instance in a guest to spawn SIOV's which is
> > useful.
> 
> Does your VF support both MSI/IMS or IMS only? 

Of course VF's support MSI..

> If it is the former can't we adopt a phased approach or parallel
> effort between forcing guest to use MSI and adding hypercall to
> enable IMS on VF? Finding a way to disable IMS is anyway required
> per earlier discussion when hypercall is not available, and it could
> still provide a functional though suboptimal model for such VFs.

Sure, I view that as the bare minimum

Jason