Re: [PATCH] x86/PVH: expose OEMx ACPI tables to Dom0

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.03.2025 11:18, Roger Pau Monné wrote:
> On Wed, Mar 26, 2025 at 10:45:18AM +0100, Jan Beulich wrote:
>> On 26.03.2025 10:21, Roger Pau Monné wrote:
>>> On Wed, Mar 26, 2025 at 09:45:09AM +0100, Jan Beulich wrote:
>>>> Further tables on said system
>>>> which weren't blacklisted prior to that commit, yet which also aren't
>>>> whitelisted are DBGP, DBG2, FIDT, LPIT, MIGT, MSCT, NITR, PCCT, RASF,
>>>> SVOS, UEFI, WDDT, and WSMT. Even without diving into the details of any
>>>> of them it seems pretty clear to me that at least some would want
>>>> whitelisting, too.
>>>
>>> I cannot find any reference about: FIDT, MIGT, NITR, SVOS and WDDT in
>>> the ACPI spec.
>>
>> WDDT - Watchdog Descriptor Table (Table 5.6 in spec version 6.5)
>>
>>> The MSCT I think we don't want to expose, as it's related to topology
>>> data.
>>>
>>> Regarding RASF I would be slightly worried about the patrol scrub
>>> feature.  The memory map exposed to dom0 will be different from the
>>> native one, and there's also the interposed p2m.
>>
>> Thing is - either kind of Dom0 needs to have a sufficient level of insight
>> into the host memory map to support memory-related RAS features. Which may
>> mean that RASF may only be exposed if the Dom0 kernel declares itself as
>> aware of the need to consider data there to refer to a separate address
>> space.
> 
> Yes, but then, how is a PVH dom0 going to be aware of such addresses?
> Given the automatic translation of gfn -> mfn that's completely hidden
> from dom0.

Right, but the knowledge is going to be necessary there, I expect.

> I'm not saying it can't be done, but I think RASF shouldn't be exposed
> to a PVH dom0 until we understand how such feature is supposed to work
> with the interposed p2m and the fabricated memory map available to a
> PVH dom0.  Note a PVH dom0 can still get the host memory map from the
> XENMEM_machine_memory_map hypercall.

Oh, of course I agree we can't expose such without first having dealt with
the implications.

Jan