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SubjectRe: [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE
On Fri, Aug 24, 2018 at 10:26:50AM -0700, Nadav Amit wrote:
> at 1:47 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> > On Thu, Aug 23, 2018 at 02:39:59PM +0100, Will Deacon wrote:
> >> The only problem with this approach is that we've lost track of the granule
> >> size by the point we get to the tlb_flush(), so we can't adjust the stride of
> >> the TLB invalidations for huge mappings, which actually works nicely in the
> >> synchronous case (e.g. we perform a single invalidation for a 2MB mapping,
> >> rather than iterating over it at a 4k granule).
> >>
> >> One thing we could do is switch to synchronous mode if we detect a change in
> >> granule (i.e. treat it like a batch failure).
> >
> > We could use tlb_start_vma() to track that, I think. Shouldn't be too
> > hard.
>
> Somewhat unrelated, but I use this opportunity that TLB got your attention
> for something that bothers me for some time. clear_fixmap(), which is used
> in various places (e.g., text_poke()), ends up in doing only a local TLB
> flush (in __set_pte_vaddr()).
>
> Is that sufficient?

Urgh.. weren't the fixmaps per cpu? Bah, I remember looking at this
during PTI, but I seem to have forgotten everything again.


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