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

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Message-ID: <59034a932606e25c0b260540fff0b6dc.squirrel@twosheds.infradead.org>
Date:   Sun, 8 Nov 2020 22:09:38 -0000
From:   "David Woodhouse" <dwmw2@...radead.org>
To:     "Thomas Gleixner" <tglx@...utronix.de>
Cc:     "Jason Gunthorpe" <jgg@...dia.com>,
        "Tian\, Kevin" <kevin.tian@...el.com>,
        "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).

In the absence of a forward-thinking design from Intel perhaps we could
use the existence of an IOMMU with interrupt remapping and not caching
mode as the indication that it's bare metal?

-- 
dwmw2