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

[Ben Catterall <Ben.Catterall@xxxxxxxxxx>]

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@xxxxxxx> 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!
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