Re: [BUG] __copy_to_user_inatomic broken on non Pentium machines
On Sun, 2007-03-25 at 11:14 -0700, Linus Torvalds wrote:
> > Environment: Pre Pentium systems, (boot_cpu_data.wp_works_ok == 0)
>
> This shouldn't be "pre-pentium", afaik. WP-works-ok on i486 too. I think
> only the original i386 had this bug ("feature").
>
> But I agree, it does seem to be broken on such machines (I assume you
> don't actually have one, but just tested by forcing it by hand ;)
Yes, it's a genuine i386 embedded system and AFAIK the same feature is
available on 486 clones. i386 and Co are still in used in the embedded
space.
tglx
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Re: [BUG] __copy_to_user_inatomic broken on non Pentium machines
* Linus Torvalds <[EMAIL PROTECTED]> wrote:
> On Sun, 25 Mar 2007, Thomas Gleixner wrote:
> >
> > Environment: Pre Pentium systems, (boot_cpu_data.wp_works_ok == 0)
>
> This shouldn't be "pre-pentium", afaik. WP-works-ok on i486 too. I
> think only the original i386 had this bug ("feature").
>
> But I agree, it does seem to be broken on such machines (I assume you
> don't actually have one, but just tested by forcing it by hand ;)
actually, AFAIK this is a genuine i386 box Thomas has (an embedded
board). Our hardware legacies and the resulting dependencies _really_
stick around for quite long time :-/
Ingo
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Re: [BUG] __copy_to_user_inatomic broken on non Pentium machines
On Sun, 25 Mar 2007, Thomas Gleixner wrote:
>
> Environment: Pre Pentium systems, (boot_cpu_data.wp_works_ok == 0)
This shouldn't be "pre-pentium", afaik. WP-works-ok on i486 too. I think
only the original i386 had this bug ("feature").
But I agree, it does seem to be broken on such machines (I assume you
don't actually have one, but just tested by forcing it by hand ;)
> Now __copy_to_user_ll() takes the (boot_cpu_data.wp_works_ok == 0) path,
> which in turn calls
>
> down_read(current->mm->mmap_sem) - which might sleep
>
> and
>
> get_user_pages() - which has a cond_resched() inside.
>
> Not sure how to fix that.
I agree. Nasty. But the thing is, it's actually much worse. We use
"__put_user()" earlier to try to fault it in writably, and that one is
totally broken on a CPU where wp_works_ok isn't set.
The whole notion that we should do this at access time is broken.
We should go back to doing it at "access_ok()", or we should just state
that we don't support original-i386 CPU's any more. As it is, we don't do
it right *anyway*, since we only do the tests properly in
__copy_to_user(), and totally miss them in __put_user() and friends.
So it's buggy on i386 however you try to fix it. The only way to fix it
properly is to move the i386 fixup early, into "access_ok()", the way it
used to be.
Linus
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Re: [BUG] __copy_to_user_inatomic broken on non Pentium machines
On Sun, 25 Mar 2007, Thomas Gleixner wrote: Environment: Pre Pentium systems, (boot_cpu_data.wp_works_ok == 0) This shouldn't be pre-pentium, afaik. WP-works-ok on i486 too. I think only the original i386 had this bug (feature). But I agree, it does seem to be broken on such machines (I assume you don't actually have one, but just tested by forcing it by hand ;) Now __copy_to_user_ll() takes the (boot_cpu_data.wp_works_ok == 0) path, which in turn calls down_read(current-mm-mmap_sem) - which might sleep and get_user_pages() - which has a cond_resched() inside. Not sure how to fix that. I agree. Nasty. But the thing is, it's actually much worse. We use __put_user() earlier to try to fault it in writably, and that one is totally broken on a CPU where wp_works_ok isn't set. The whole notion that we should do this at access time is broken. We should go back to doing it at access_ok(), or we should just state that we don't support original-i386 CPU's any more. As it is, we don't do it right *anyway*, since we only do the tests properly in __copy_to_user(), and totally miss them in __put_user() and friends. So it's buggy on i386 however you try to fix it. The only way to fix it properly is to move the i386 fixup early, into access_ok(), the way it used to be. Linus - 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: [BUG] __copy_to_user_inatomic broken on non Pentium machines
* Linus Torvalds [EMAIL PROTECTED] wrote: On Sun, 25 Mar 2007, Thomas Gleixner wrote: Environment: Pre Pentium systems, (boot_cpu_data.wp_works_ok == 0) This shouldn't be pre-pentium, afaik. WP-works-ok on i486 too. I think only the original i386 had this bug (feature). But I agree, it does seem to be broken on such machines (I assume you don't actually have one, but just tested by forcing it by hand ;) actually, AFAIK this is a genuine i386 box Thomas has (an embedded board). Our hardware legacies and the resulting dependencies _really_ stick around for quite long time :-/ Ingo - 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: [BUG] __copy_to_user_inatomic broken on non Pentium machines
On Sun, 2007-03-25 at 11:14 -0700, Linus Torvalds wrote: Environment: Pre Pentium systems, (boot_cpu_data.wp_works_ok == 0) This shouldn't be pre-pentium, afaik. WP-works-ok on i486 too. I think only the original i386 had this bug (feature). But I agree, it does seem to be broken on such machines (I assume you don't actually have one, but just tested by forcing it by hand ;) Yes, it's a genuine i386 embedded system and AFAIK the same feature is available on 486 clones. i386 and Co are still in used in the embedded space. tglx - 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/
