Re: [PATCH 5/7] x86/mmu: Allocate/free PASID

Jacob Pan (Jun)
2020-04-28T20:42:07Z

On Tue, 28 Apr 2020 12:07:25 -0700
"Luck, Tony" <tony.luck@intel.com> wrote:

> > If fd release cleans up then how should there be something in
> > flight at the final mmdrop?
>
> ENQCMD from the user is only synchronous in that it lets the user
> know their request has been added to a queue (or not). Execution of
> the request may happen later (if the device is busy working on
> requests for other users). The request will take some time to
> complete. Someone told me the theoretical worst case once, which I've
> since forgotten, but it can be a long time.
>
> So the driver needs to use flush/drain operations to make sure all
> the in-flight work has completed before releasing/re-using the PASID.
>
Are you suggesting we should let driver also hold a reference of the
PASID?

> -Tony