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

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Date:   Wed, 11 Nov 2020 15:41:59 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Gunthorpe <jgg@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
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        "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>,
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        "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 Sun, Nov 08, 2020 at 07:36:34PM +0000, David Woodhouse wrote:
> So it does look like we're going to need a hypercall interface to
> compose an MSI message on behalf of the guest, for IMS to use. In fact
> PCI devices assigned to a guest could use that too, and then we'd only
> need to trap-and-remap any attempt to write a Compatibility Format MSI
> to the device's MSI table, while letting Remappable Format messages get
> written directly.
> 
> We'd also need a way for an OS running on bare metal to *know* that
> it's on bare metal and can just compose MSI messages for itself. Since
> we do expect bare metal to have an IOMMU, perhaps that is just a
> feature flag on the IOMMU?

Have the platform firmware advertise if it needs native or virtualized
IMS handling.  If it advertises neither don't support IMS?