Re: [PATCH v1 08/40] i386/tdx: Adjust the supported CPUID based on TDX restrictions

Xiaoyao Li
2022-08-25T12:44:53Z

On 8/25/2022 7:26 PM, Gerd Hoffmann wrote:
> Hi,
>
>> between VMM and TDs. Adjust supported CPUID for TDs based on TDX
>> restrictions.
>
> Automatic adjustment depending on hardware capabilities isn't going to
> fly long-term, you'll run into compatibility problems sooner or later,
> for example when different hardware with diverging capabilities (first
> vs. second TDX generation) leads to different CPUID capsets in a
> otherwise identical configuration.
>
> Verification should happen of course, but I think qemu should just throw
> an error in case the tdx can't support a given cpu configuration.

I think you misunderstand this patch.

It's to adjust the supported feature set of the platform, not the
feature set of the given VM/TD. I.e, the adjusted supported feature set
will be used to *verify* the VM's setting that specified by user. Of
course, if user requires unsupported feature, QEMU will throw an error.

> (see also Daniels reply to the cover letter).
>
> take care,
> Gerd
>