On Wed, Oct 12, 2022 at 10:34:23AM +0000, Radovanovic, Aleksandar wrote:

For the MSI EventID, the HW interrupt logic assumes the MSI write value is 
equal to the MSI vector number. However, the vector number is programmable
for most (all) of the interrupt sources, which isn't exactly the same as saying
EventID is programmable for a vector number, but can be used to emulate the
desired behaviour, with a translation table in firmware. 

If you do this stuff wrong you will eventually run into situations
that don't work. Like VFIO/VMs and things.

As for GITS_TRANSLATER, we can take up to 4 different IOVAs, which limits us
to 4 CDX devices (should be sufficient for current HW use-cases). Also, it means
that the address part must be the same for all vectors within a single CDX 
device. I'm assuming this is OK as it is going to be a single interrupt and IOMMU
domain anyway.

This is not at all how MSI is supposed to work.

Jason

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