Re: TLB flushes on fixmap changes

[Linus Torvalds]

On Fri, Aug 24, 2018 at 11:36 AM Nadav Amit <nadav.amit@xxxxxxxxx> wrote:
>
> >
> > Urgh.. weren't the fixmaps per cpu? Bah, I remember looking at this
> > during PTI, but I seem to have forgotten everything again.
>
> [ Changed the title. Sorry for hijacking the thread. ]
>
> Since:
>
> native_set_fixmap()->set_pte_vaddr()->pgd_offset_k()

The fixmaps should be entirely fixed after bootup to constant
mappings, except for the KMAP ones, and they are indexed per-cpu.

That's what my mental model is, at least.

Can you actually find something that changes the fixmaps after boot
(again, ignoring kmap)?

Maybe worth adding some debugging to verify that?

                Linus