Re: x86_64: potential critical issue with quicklists and pagetable pages

From: Benjamin Herrenschmidt
Date: Mon Sep 24 2007 - 17:28:45 EST

On Fri, 2007-09-21 at 12:21 -0700, 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).
> 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.
> As it is, the quicklists try to be something separate, but by virtue of
> being separate, they will always be buggy.
> 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.

I've been mostly offline since KS (since a bit before in fact), so I
missed some of those discussions but so that you know, I'm toying a bit
with mmu gather and page table accessors at the moment, and one of the
things I've been contemplating is just that ... integrating a quicklist
in the gather to handle just that (and possibly other issues that have
been overlooked on some archs).

I'd suggest just reverting the patch for now (well, I see from the
commit list that you did just that) and I'll try to come up with
something better.

Christoph, I'd be happy if you didn't start butchering mmu_gather just
right now since I'm doing just that and it will collide all over the
place :-) Or if you want something specific done, please throw
ideas/patches at me and I'll integrate that in my serie.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at