Re: [PATCH 4/5] x86: Allow nesting of the debug stack IDT setting

["H. Peter Anvin" <hpa@zytor.com>]

On 05/31/2012 01:56 PM, Steven Rostedt wrote:
> On Thu, 2012-05-31 at 13:39 -0700, H. Peter Anvin wrote:
>> On 05/31/2012 01:35 PM, Steven Rostedt wrote:
>>>
>>> Thus only the debug stack does the stack TSS trick.
>>>
>>> Is this what you were looking for? (God, it just shows how much time
>>> I've been spending on this crap, as I was able to find all this by
>>> memory and not grepping for it :-p )
>>>
>>
>> That's why I asked instead of pulled it up myself.
>>
>> However, what is missing is what the permitted transitions are.  This
>> affects the options.
> 
> Only the debug stack changes. These happen in the two places I already
> mentioned.
> 
> One, the switch of the IDT in NMI (to convert the IST from 4 to 0, and
> just keep the same stack).
> 
> Two, is the trick in the paranoidzeroentry_ist code (adding the debug
> stack). That changes the DEBUG stack pointer.
> 

No, I'm asking what environments (alternate stacks) are permitted where.
 That is the important information.

The interaction of the above two things is part of the problem, of
course, and I think it can (and should) be avoided.

	-hpa