From: Jason Gunthorpe <jgg@nvidia.com>
Sent: Thursday, August 5, 2021 7:27 PM

On Wed, Aug 04, 2021 at 10:59:21PM +0000, Tian, Kevin wrote:

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From: Jason Gunthorpe <jgg@nvidia.com>
Sent: Wednesday, August 4, 2021 10:05 PM

On Mon, Aug 02, 2021 at 02:49:44AM +0000, Tian, Kevin wrote:

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Can you elaborate? IMO the user only cares about the label (device

cookie

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plus optional vPASID) which is generated by itself when doing the

attaching

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call, and expects this virtual label being used in various spots

(invalidation,

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page fault, etc.). How the system labels the traffic (the physical RID or

RID+

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PASID) should be completely invisible to userspace.

I don't think that is true if the vIOMMU driver is also emulating
PASID. Presumably the same is true for other PASID-like schemes.

I'm getting even more confused with this comment. Isn't it the
consensus from day one that physical PASID should not be exposed
to userspace as doing so breaks live migration?

Uh, no?

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with PASID emulation vIOMMU only cares about vPASID instead of
pPASID, and the uAPI only requires user to register vPASID instead
of reporting pPASID back to userspace...

vPASID is only a feature of one device in existance, so we can't make
vPASID mandatory.

sure. my point is just that if vPASID is being emulated there is no need
of exposing pPASID to user space. Can you give a concrete example
where pPASID must be exposed and how the user wants to use this
information? 

Thanks
Kevin