Re: [PATCH] x86/mm: Check cc_vendor when printing memory encryption info

[Borislav Petkov <bp@alien8.de>]

On Thu, Nov 09, 2023 at 07:41:33PM +0100, Jeremi Piotrowski wrote:
> tdx_early_init() changes kernel behavior with the assumption that it
> can talk directly to the TD module or change page visibility in
> a certain way, instead of talking to a paravisor. So that CPUID is
> hidden to prevent this.  Otherwise tdx_early_init() would need to be
> modified to check "am I running with TD partitioning and if so
> - switch to other implementations".

Here we go with the virt zoo again. If you hide TDX_CPUID_LEAF_ID from
it, then it of course doesn't know that it is a TDX guest. This is the
same thing as the SNP vTom thing: the only viable way going forward is
for the guest kernel to detect correctly what it runs on and act
accordingly.

You can't just do some semi-correct tests for vendor - correct only
if you squint hard enough - and hope that it works because it'll break
apart eventually, when that second-level TDX fun needs to add more
hackery to the guest kernel.

So, instead, think about how the paravisor tells the guest it is running
on one - a special CPUID leaf or an MSR in the AMD case - and use that
to detect it properly.

Everything else is a mess waiting to happen.

Thx.

-- 
Regards/Gruss,
    Boris.

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