Re: [PATCH Part2 v6 09/49] x86/fault: Add support to handle the RMP fault for user address

Borislav Petkov
2022-09-03T04:25:44Z

On Fri, Sep 02, 2022 at 03:33:20PM +0000, Kalra, Ashish wrote:
> Yes we want to map the faulting address to a RMP entry, but hugepage
> entries in RMP table are basically subpage 4K entries. So it is a 4K
> entry when the page is a 2M one and also a 4K entry when the page is a
> 1G one.

Wait, what?!

APM v2 section "15.36.11 Large Page Management" and PSMASH are then for
what exactly?

> That's why the computation to get a 4K page index within a 2M/1G
> hugepage mapping is required.

What if a guest RMP-faults on a 2M page and there's a corresponding 2M
RMP entry? What do you need the 4K entry then for?

Hell, __snp_lookup_rmpentry() even tries to return the proper page
level...

/me looks in disbelief in your direction...

Thx.

--
Regards/Gruss,
Boris.