Re: [patch V9 00/39] x86/entry: Rework leftovers (was part V)

From: Peter Zijlstra
Date: Thu Jun 04 2020 - 09:26:41 EST

On Wed, Jun 03, 2020 at 08:18:44PM +0100, Andrew Cooper wrote:

> Well that didn't last long...
> The new ISE (rev 39, published today) introduces BUS LOCK DEBUG
> EXCEPTION which is now a second inverted polarity sticky bit (bit 11) in
> %dr6.
> This one is liable to get more traction than RTM debugging, so something
> probably does want fixing in the #DB handler.

Well that's crap :-(

It being enabled through IA32_DEBUGCTL instead of through DR7 means that
the current code doesn't disable it and this then means we can have
nested #DB again.

Who sodding throught this was a good idea ?! What happened to #AC that
SLD currently uses?

What hardware will this be in and can we get this fixed?