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

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Message-ID: <87k0uvk0oc.fsf@nanos.tec.linutronix.de>
Date:   Sun, 08 Nov 2020 22:18:11 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jason Gunthorpe <jgg@...dia.com>,
        "Tian\, Kevin" <kevin.tian@...el.com>
Cc:     "Jiang\, Dave" <dave.jiang@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        "vkoul\@kernel.org" <vkoul@...nel.org>,
        "Dey\, Megha" <megha.dey@...el.com>,
        "maz\@kernel.org" <maz@...nel.org>,
        "bhelgaas\@google.com" <bhelgaas@...gle.com>,
        "alex.williamson\@redhat.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\@intel.com" <jing.lin@...el.com>,
        "Williams\, Dan J" <dan.j.williams@...el.com>,
        "kwankhede\@nvidia.com" <kwankhede@...dia.com>,
        "eric.auger\@redhat.com" <eric.auger@...hat.com>,
        "parav\@mellanox.com" <parav@...lanox.com>,
        "rafael\@kernel.org" <rafael@...nel.org>,
        "netanelg\@mellanox.com" <netanelg@...lanox.com>,
        "shahafs\@mellanox.com" <shahafs@...lanox.com>,
        "yan.y.zhao\@linux.intel.com" <yan.y.zhao@...ux.intel.com>,
        "pbonzini\@redhat.com" <pbonzini@...hat.com>,
        "Ortiz\, Samuel" <samuel.ortiz@...el.com>,
        "Hossain\, Mona" <mona.hossain@...el.com>,
        "dmaengine\@vger.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci\@vger.kernel.org" <linux-pci@...r.kernel.org>,
        "kvm\@vger.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection

On Fri, Nov 06 2020 at 09:14, Jason Gunthorpe wrote:
> On Fri, Nov 06, 2020 at 09:48:34AM +0000, Tian, Kevin wrote:
> For instance you could put a "disable IMS" flag in the ACPI tables, in
> the config space of the emuulated root port, or any other areas that
> clearly belong to the platform.
>
> The OS logic would be
>  - If no IMS information found then use IMS (Bare metal)
>  - If the IMS disable flag is found then
>    - If (future) hypercall available and the OS knows how to use it
>      then use IMS
>    - If no hypercall found, or no OS knowledge, fail IMS

That does not work because an older hypervisor would not have that
disable flag and the guest kernel would assume to be on bare metal (if
no other indicators are there).

Thanks

        tglx