Re: K8 Errata #93: adjusting address to a fixup block

[Andi Kleen <ak@muc.de>]

Alexandre Oliva <aoliva@redhat.com> writes:

> While I investigated the problem of probing the touchpad on a Compaq
> Presario r3004, I'd sometimes get the K8 Errata #93 warning.  One of
> my theories was that we might be missing some fix up because of the
> Errata, or adjusting an address that wasn't the current-instruction

It's more likely the BIOS is executing SMM code to handle
the touch pad and that SMM code doesn't have the correct
workaround for the erratum.

> address, so I came up with this patch.  It turned out to make no
> difference, but it still feels like an improvement to me, since some
> day we might be resuming from halt into a fix-up block.  Thoughts?

The code is already ugly enough and handles most of the cases, 
I don't think it is worth it complicating it even more just
to handle more corner cases of buggy BIOS.

The real fix is to fix your BIOS.

 	static int warned;
+	if ((error_code & 16) == 0)
+		return 0;

This is dubious because the I/D bit is undefined when NX is disabled
in EFER (e.g. with noexec=off or when the CPU doesn't support NX)

-Andi