[PATCH 3/6] qemu: check if AMD secure guest support is enabled

[Boris Fiuczynski]

On 5/12/20 5:32 PM, Erik Skultety wrote:
I leave 1) and 2) to the AMD experts... :-)

>>> 3) Check if Qemu supports SEV feature (maybe we can detect the existence
>>> of the query-sev QMP command or detect Qemu version >= 2.12)
> ^This is already achieved by qemuMonitorJSONGetSEVCapabilities
> 
>> The idea is to check the host capabilities to detect if qemus capabilities
>> need to be reprobed. Therefore this would be a result if checks 1+2 change
>> but it would not be a cache invalidation trigger.
> I agree in the sense that the SEV support that is currently being reported in
> QEMU capabilities wasn't a good choice because it reports only platform data
> which are constant to the host and have nothing to do with QEMU. It would be
> okay to just say <sev supported="yes|no"/> in qemu capabilities and report the
> rest in host capabilities. I haven't added this info into host capabilities
> when I realized the mistake because I didn't want to duplicate the platform
> info on 2 places.  For the IBM secure guest feature, it makes total sense to
> report support within host capabilities, I'm just not sure whether we should do
> the same for SEV and try really hard to "fix" the mess.

I am not sure I understand the "mess" correctly.
The idea is to prevent the cached qemu capabilities becoming stale which 
Daniel PB has called earlier a bug in the caching algorithm. This can 
occur if the kernel or firmware configuration change. To find out these 
situations we try to implement qemu capability cache invalidation 
triggers. The monitor method you mentioned is called during a (re-)probe 
and for IBM Secure Execution the host CPU model is also updated during a 
(re-)probe. Wouldn't that clean up the "mess"?

-- 
Mit freundlichen Grüßen/Kind regards
    Boris Fiuczynski

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