Re: [Xen-devel] [PATCH 3/2] x86/desc: Drop __HYPERVISOR_CS32

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.08.2019 17:36, Andrew Cooper wrote:
> On 09/08/2019 13:50, Jan Beulich wrote:
> > On 09.08.2019 14:39, Andrew Cooper wrote:
> > > Xen, being 64bit only these days, has no use for a 32bit Ring 0 code
> > > segment.
> > >
> > > Delete __HYPERVISOR_CS32 and remove it from the GDTs.  Also delete
> > > __HYPERVISOR_CS64 and use __HYPERVISOR_CS uniformly.
> > Long, long ago we've been considering doing this. Agreed,
> > nothing has surfaced to actually use it, but I wouldn't
> > subscribe to "has no use": We will need it if we ever want
> > to be able to run on 32-bit EFI _and_ invoke runtime
> > services there. Back then through the consideration against
> > dropping it was that we may want to invoke 32-bit BIOS
> > services (PCI, VGA) from the hypervisor.
> I hadn't realised these had even been considered in the past.  I don't
> think either of these are likely to happen now.
>
> As for the text, Xen really does have no users of a 32bit R0 code
> segment, and the statement does not preclude the fact that there may be
> legitimate uses for CS32.
>
> Would you be happier with "days, and does not use a 32bit Ring 0 code
> segment." ?
Yes, "does not use" is definitely more correct imo, as would be
"has no user" (note the extra "r" compared to your original text;
your reply makes me wonder whether it was simply a typo).

Jan

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel