Re: [RFC][PATCH 2/6] mm: Change flush_tlb_range() to take an mm_struct

[Rik van Riel]

On 03/02/2011 02:19 PM, Linus Torvalds wrote:

> > There are various reasons that we need to flush TLBs _after_ freeing
> > the page-tables themselves. For some architectures (x86 among others)
> > this serializes against (both hardware and software) page table
> > walkers like gup_fast().
>
> This part of the changelog also makes no sense what-so-ever. It's
> actively wrong.
>
> On x86, we absolutely *must* do the TLB flush _before_ we release the
> page tables. So your commentary is actively wrong and misleading.
>
> The order has to be:
>   - clear the page table entry, queue the page to be free'd
>   - flush the TLB
>   - free the page (and page tables)
>
> and nothing else is correct, afaik. So the changelog is pure and utter
> garbage. I didn't look at what the patch actually changed.

The patch seems to preserve the correct behaviour.

The changelog should probably read something along the
lines of:

"There are various reasons that we need to flush TLBs _after_
 clearing the page-table entries themselves."
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