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

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

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).


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