Re: pgd_none_or_clear_bad strangeness?
On Wed, Oct 03, 2007 at 07:18:23PM +0100, Hugh Dickins wrote:
> 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.
Indeed, that's precisely what's happening. I'm walking one page past
the end of userspace.
And the reason is I changed my walker from using for loops to do/while
loops at Nick's insistance, so start==end no longer gets noticed
immediately. This also explains why the bug doesn't manifest in
lguest: no PSE mappings.
Thanks, guys!
--
Mathematics is the supreme nostalgia of our time.
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Re: 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
-
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Re: pgd_none_or_clear_bad strangeness?
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.
>
> Has something changed here? I'm pretty sure this used to work! Is this
> 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?).
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: pgd_none_or_clear_bad strangeness?
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.
Has something changed here? I'm pretty sure this used to work! Is this
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?).
-
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: 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
-
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the body of a message to [EMAIL PROTECTED]
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Please read the FAQ at http://www.tux.org/lkml/
Re: pgd_none_or_clear_bad strangeness?
On Wed, Oct 03, 2007 at 07:18:23PM +0100, Hugh Dickins wrote:
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.
Indeed, that's precisely what's happening. I'm walking one page past
the end of userspace.
And the reason is I changed my walker from using for loops to do/while
loops at Nick's insistance, so start==end no longer gets noticed
immediately. This also explains why the bug doesn't manifest in
lguest: no PSE mappings.
Thanks, guys!
--
Mathematics is the supreme nostalgia of our time.
-
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
pgd_none_or_clear_bad strangeness?
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.
Has something changed here? I'm pretty sure this used to work! Is this
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.
--
Mathematics is the supreme nostalgia of our time.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
pgd_none_or_clear_bad strangeness?
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.
Has something changed here? I'm pretty sure this used to work! Is this
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.
--
Mathematics is the supreme nostalgia of our time.
-
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
