RE: [PATCH v3 6/8] admin: Add theory of operation for write recording commands

[Parav Pandit <parav@nvidia.com>]

Hi Michael,

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Thursday, November 9, 2023 1:29 PM

[..]
> > Besides the issue of performance, it's also racy, assuming we are logging
> IOVA.
> >
> > 0) device log IOVA
> > 1) hypervisor fetches IOVA from log buffer
> > 2) guest map IOVA to a new GPA
> > 3) hypervisor traverse guest table to get IOVA to new GPA
> >
> > Then we lost the old GPA.
> 
> Interesting and a good point. And by the way e.g. vhost has the same issue.  You
> need to flush dirty tracking info when changing the mappings somehow.  Parav
> what's the plan for this? Should be addressed in the spec too.
> 
As you listed the flush is needed for vhost or device-based DPT.
The necessary plumbing is already covered for this in the query (read and clear) command of this v3 proposal.
It is listed in Device Write Records Read Command.

When the page write record is fully read, it is flushed.
How/when to use, I think its hypervisor specific, so we probably better off not documenting those details.
May be such read is needed in some other path too depending on how hypervisor implemented.