lkml.org 
[lkml]   [2007]   [Oct]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: pgd_none_or_clear_bad strangeness?
On Wed, 3 Oct 2007, Nick Piggin wrote:
> On Tue, Oct 02, 2007 at 05:20:03PM -0500, Matt Mackall wrote:
> > In lib/pagewalk.c, I've been using the various forms of
> > {pgd,pud,pmd}_none_or_clear_bad while walking page tables as that
> > seemed the canonical way to do things. Lately (eg with -rc7-mm1),
> > these have been triggering messages like "bad pgd 0x01e3" and causing
> > nasty double faults. It appears this is actually triggered at the pmd
> > level (mm/memory.c:116), though it appears to produce the wrong
> > message.

I guess the "wrong message" is an artifact of pud/pmd folding;
but I get too confused by the different levels myself to want to
think more about it - I'll just assume it's "right" somehow ;)

> >
> > Has something changed here? I'm pretty sure this used to work! Is this

I don't know of anything changing here, sorry.

> > not a kosher thing to do? Does it make any sense I'd repeatedly run
> > into a bad pmd in the middle of bash's page table right after boot?
> > The simple _none variant seems to work, but I worry that it's papering
> > over a real problem.
>
> No, I think that should be the right thing to do for userspace pages.
> You're not walking into a hugetlb area or a kernel mapping are you?
> (the bad pgd: line could be important... 0x01e3 would be a linear kernel
> mapping I think?).

I should have spent more time reading Nick's reply and less time trying
to work it out for myself! Yes, that's the conclusion I came to, for
some reason you're now going beyond the user vmas and walking into the
linear kernel mapping, which has _PAGE_GLOBAL and _PAGE_PSE bits set.

Hugh
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-10-03 20:21    [W:0.044 / U:0.360 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site