Re: XENMAPSPACE_grant_table vs. GNTTABOP_setup_table

[Martin Lucina <martin@xxxxxxxxxx>]

On Wednesday, 10.06.2020 at 15:21, Andrew Cooper wrote:
> > I don't need v2 at all, I was just going by the comments in grant_table.h,
> > which read: "Version 1 of the grant table entry structure is maintained
> > purely for backwards compatibility.  New guests should use version 2."
> 
> Ha...
> 
> That comment wasn't written with the benefit of hindsight.
> 
> IMO, grant v2 is not worth the astounding quantity of XSAs its
> implementation actually gave us, or the complexity of the resulting code.
> 
> > Grant status frames are a v2-only thing, right?
> 
> Correct.
> 
> The split status frames was new in v2, in an attempt to reduce cacheline
> ping-pong.
> 
> The downside is that the guest needs an unbounded loop trying to make a
> change to the grant table while ensuring that the flags in the status
> frame don't change asynchronously.
> 
> ~Andrew
> 
> P.S. In some theoretical world, I was hoping to have something to live
> in https://xenbits.xen.org/docs/latest/guest-guide/index.html on this
> subject.  Do you mind if I use you as a retroactive guineapig if/when
> some documentation were to appear?

No problem, sure, go for it.

-mato