Re: [RFC 01/20] mm/tlb: fix fullmm semantics

Will Deacon
2021-02-03T09:46:22Z

On Tue, Feb 02, 2021 at 01:35:38PM -0800, Nadav Amit wrote:
> > On Feb 2, 2021, at 3:00 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Tue, Feb 02, 2021 at 01:32:36AM -0800, Nadav Amit wrote:
> >>> On Feb 1, 2021, at 3:36 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >>>
> >>>
> >>> https://lkml.kernel.org/r/20210127235347.1402-1-will@kernel.org
> >>
> >> I have seen this series, and applied my patches on it.
> >>
> >> Despite Will’s patches, there were still inconsistencies between fullmm
> >> and need_flush_all.
> >>
> >> Am I missing something?
> >
> > I wasn't aware you were on top. I'll look again.
>
> Looking on arm64’s tlb_flush() makes me think that there is currently a bug
> that this patch fixes. Arm64’s tlb_flush() does:
>
> /*
> * If we're tearing down the address space then we only care about
> * invalidating the walk-cache, since the ASID allocator won't
> * reallocate our ASID without invalidating the entire TLB.
> */
> if (tlb->fullmm) {
> if (!last_level)
> flush_tlb_mm(tlb->mm);
> return;
> }
>
> But currently tlb_mmu_finish() can mistakenly set fullmm incorrectly (if
> mm_tlb_flush_nested() is true), which might skip the TLB flush.

But in that case isn't 'freed_tables' set to 1, so 'last_level' will be
false and we'll do the flush in the code above?

Will