Re: [PATCH Part2 v6 07/49] x86/sev: Invalid pages from direct map when adding it to RMP table

Borislav Petkov
2022-12-19T20:09:33Z

On Mon, Dec 19, 2022 at 09:00:26AM -0600, Michael Roth wrote:
> We implemented this approach for v7, but it causes a fairly significant
> performance regression, particularly for the case for npages > 1 which
> this change was meant to optimize.
>
> I still need to dig in a big but I'm guessing it's related to flushing
> behavior.

Well, AFAICT, change_page_attr_set_clr() flushes once at the end.

Don't you need to flush when you modify the direct map?

> It would however be nice to have a set_direct_map_default_noflush()
> variant that accepted a 'npages' argument, since it would be more
> performant here and also would potentially allow for restoring the 2M
> direct mapping in some cases. Will look into this more for v8.

set_pages_direct_map_default_noflush()

I guess.

Although the name is a mouthful so I wouldn't mind having those
shortened.

In any case, as long as that helper is properly defined and documented,
I don't mind.

Thx.

--
Regards/Gruss,
Boris.