Re: [RFC 3/4] HVM x86 deprivileged mode: Code for switching into/out of deprivileged mode

[Ben Catterall <Ben.Catterall@citrix.com>]

On 18/08/15 11:25, Ben Catterall wrote:
>
>
> On 17/08/15 16:17, Jan Beulich wrote:
>>>>> On 17.08.15 at 17:07, <tim@xen.org> wrote:
>>> At 14:53 +0100 on 17 Aug (1439823232), Ben Catterall wrote:
>>>> So, have we arrived at a decision for this? Thanks!
>>>
>>> Seems to have stalled a bit.  OK, I propose that:
>>>   - we use TR/IST to make Xen take interrupts/exceptions at a
>>> different SP;
>>>   - we make that SP be an extension of the main stack, so that things
>>>     like current() Just Work[tm];
>  From Xen's cpu stack layout, page 4 is currently unused so I'll put it
> here. Is this an acceptable?
Or, would it be better to put it at position 5, and move the optional 
MEMORY_GUARD page down to position 4?
>>>   - we set this up and tear it down when we enter/leave depriv mode.
>>>   - someone ought to look at the case where IST handlers copy
>>>     themselves to the main stack, and see if we need to adjust that too.
>>>
>>> Any other proposals?
>>
>> No.
>>
>
>
>>> I think we can leave the question of TR switching on VMEXIT as a
>>> separate issue.
>>
>> Just like for the other one - at this point I think anything that work
>> should be okay. Dealing with quirks can be deferred (but it would
>> be nice if a respective note was added in a prominent place so it
>> doesn't get forgotten once/if these patches leave RFC state).
>>
>> Jan
>>
> Ok, thanks all!