Re: [PATCH 1/4] xen/xsm: Add XSM_HW_PRIV

[Jason Andryuk <jason.andryuk@amd.com>]

On 2025-06-11 09:02, Jan Beulich wrote:
> On 11.06.2025 00:57, Jason Andryuk wrote:
>> Xen includes disctinct concepts of a control domain (privileged) and a
>> hardware domain, but there is only a single XSM_PRIV check.  For dom0
>> this is not an issue as they are one and the same.
>>
>> With hyperlaunch and its build capabilities, a non-privileged hwdom and a
>> privileged control domain should be possible.  Today the hwdom fails the
>> XSM_PRIV checks for hardware-related hooks which it should be allowed
>> access to.
>>
>> Introduce XSM_HW_PRIV, and use it to mark many of the physdev_op and
>> platform_op.  The hwdom is allowed access for XSM_HW_PRIV.
>>
>> Make XSM_HW_PRIV a new privilege level that is given to the hardware
>> domain, but is not exclusive.  The control domain can still execute
>> XSM_HW_PRIV commands.  This is a little questionable since it's unclear
>> how the control domain can meaningfully execute them.  But this approach
>> is chosen to maintain the increasing privileges and keep control domain
>> fully privileged.
> 
> I consider this conceptually wrong. "Control" aiui refers to software
> (e.g. VMs or system-wide settings), but there ought to be a (pretty?)
> clear boundary between control and hardware domains, imo. As to
> "pretty" - should any overlap be necessary (xms_machine_memory_map()
> comes to mind), such would need handling specially then, I think. At
> the same time: The more of an overlap there is, the less clear it is
> why the two want/need separating in the first place.

So you are in favor of splitting control and hardware into distinct 
sets?  I am okay with this.  I implemented that originally, but I 
started doubting it.  Mainly, should control be denied any permission?

We aren't using the toolstack to build domains - dom0less or Hyperlaunch 
handles that.  This avoids issues that might arise from running the 
toolstack.

Thanks for your feedback.

-Jason