Re: [patch] SMP alternatives

[H. Peter Anvin]

Andi Kleen wrote:
> On Wed, Nov 23, 2005 at 02:15:24PM -0800, Linus Torvalds wrote:
>
> > On Wed, 23 Nov 2005, Andi Kleen wrote:
> >
> > > > THAT is what I'd like to have CPU support for. Not for UP (it's going 
> > > > away), and not for the kernel (it's never single-threaded).
> > >
> > > There is one reasonly interesting special case that will probably stay
> > > around: single CPU guest in a virtualized environment.
> >
> > .. and then the _virtualizer_ should just set the bit. 
>
> That wouldn't work if it's limited limited to ring 3.
>
> Also currently at least the Xen the driver interfaces seem to 
> rely on lock, but perhaps that can be changed.

Well, with VTX or Pacifica virtualization is in ring 3.  The fact that 
Xen isn't is a workaround for current hardware, so when we're talking 
about new hardware it's pointless.

What you really want is one bit for kernel mode (cpl 0-2) and one for 
user mode (cpl 3).

	-hpa
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