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

[David Woodhouse]

> 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