Re: crashme fault

Randy Dunlap
2007-09-17T20:05:30Z

On Mon, 17 Sep 2007 07:53:50 -0700 (PDT) Linus Torvalds wrote:

> On Mon, 17 Sep 2007, Randy Dunlap wrote:
> >
> > OK, I haven't done the microcode update yet. I ran crashme overnight
> > with your newer patch and it crashed:
>
> Well, duh.
>
> That's because I forgot to do the "error_code & PF_USER" =>
> "user_mode_vm(regs)" thing in the most common case - the
> "bad_area_nosemaphore" if-statement.
>
> But thinking more about it, it's actually just easier and more
> straightforward to just take the same approach that my original hack did,
> namely to just set PF_USER if the register state implies it was in user
> mode.
>
> So ignore that patch. You're better off with my original one that also
> gave debugging info, and if we decide that this really looks like a CPU
> buglet, the patch to actually commit would be a simplified version of that
> (appended, just FYI).

[switched email address due to some unknown problems]

Reverted that patch. Loaded new microcode update file.
Ran test for 3 hours without a fault.

It all seems rather inconclusive to me, still, the new patch (below)
makes sense.

> Also, I changed my mind on the microcode update - if you have a newer
> microcode, go ahead and try it, because if that fixes the issue, then we
> can really just close this as a "unimportant CPU bug" with the patch
> below.
>
> Linus
>
> ---
> arch/x86_64/mm/fault.c | 7 +++++++
> 1 files changed, 7 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86_64/mm/fault.c b/arch/x86_64/mm/fault.c
> index 327c9f2..54816ad 100644
> --- a/arch/x86_64/mm/fault.c
> +++ b/arch/x86_64/mm/fault.c
> @@ -374,6 +374,13 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
> if (unlikely(in_atomic() || !mm))
> goto bad_area_nosemaphore;
>
> + /*
> + * User-mode registers count as a user access even for any
> + * potential system fault or CPU buglet.
> + */
> + if (user_mode_vm(regs))
> + error_code |= PF_USER;
> +
> again:
> /* When running in the kernel we expect faults to occur only to
> * addresses in user space. All other faults represent errors in the
> -

---
~Randy
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