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SubjectRe: x86_64: potential critical issue with quicklists and page table pages
On Fri, 21 Sep 2007, Linus Torvalds wrote:

> Yeah, and the whole thing seems totally bogus. It totally depends on
> mmu_gather doing everything right (which very much includes the dependency
> on mmu gathering disabling preempt).

The quicklists have been existing for a long time in this relationship
and were actually developed initially (by Dave Miller I believe) to work
this way. The generic TLB flushing thing may have developed in parallel on
other platforms that did not use quicklists.

> For exmaple, if we were to go back to the original small tlb_gather with a
> simple quicklist on the stack, rather than the per-cpu datastructure, the
> quicklists would immediately break horribly - simply because they are
> incorrectly now depending on the internal semantics of that tlb-gather.

Hmmmm.. Right the integration of the approaches that have now diverged on
various platforms could be better.
> As it is, the quicklists try to be something separate, but by virtue of
> being separate, they will always be buggy.

I guess we need to re-join what was separated by developments on different
platforms.

> The only way to fix it would be to integrate the quicklist stuff *with*
> the mmu_gather stuff, so that these kinds of implementation issues are
> explicitly shown in the relationship, instead of havign two "independent"
> pieces of code where one piece very subtly depends on the exact
> implementation of the other.

Right. But will that not mean that quicklists would have to be used on all
platforms in a generic way?
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