Re: [RFC PATCH] docs/about/deprecated: Deprecate 32-bit host systems

[Alex Bennée]

Reinoud Zandijk <reinoud@NetBSD.org> writes:

> On Wed, Feb 22, 2023 at 09:51:57AM +0000, Daniel P. Berrangé wrote:
>> On Wed, Feb 22, 2023 at 09:11:13AM +0000, Bernhard Beschow wrote:
>> > Are there any plans or ideas to support 128 bit architectures
>> > such as CHERI in the future? There is already a QEMU fork
>> > implementing CHERI for RISC V [1]. Also ARM has developed an
>> > experimental hardware implementation of CHERI within the Morello
>> > project where Linaro is involved as well, although the QEMU
>> > implementation is performed by the University of Cambridge [2].
>> 
>> If 128 bit hardware exists and has real world non-toy usage,
>> then a request to support it in QEMU is essentially inevitable.
>> 
>> > I'm asking because once we deeply bake in the assumption that
>> > host size >= guest size then adding such architectures will
>> > become much harder.
>> 
>> Yep, that is a risk.
>
> I can second that. Better keep it in the code and deal with it. Maybe those
> specific parts can be implemented in such a way that it can easily become a
> noop on host size >= guest size.

AIUI these don't expose bigger addresses or natural atomic sizes which
is where things get tricky for the TCG. All the extra bits are used for
authentication or permission checks.

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro