Re: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range to map as encrypted

[Borislav Petkov]

On Wed, Feb 22, 2023 at 02:54:47PM -0800, Sean Christopherson wrote:
> Why?  I genuinely don't understand the motivation for bundling all of this stuff
> under a single "feature".

It is called "sanity".

See here:

https://lore.kernel.org/r/Y%2B5immKTXCsjSysx@xxxxxxx

We support SEV, SEV-ES, SEV-SNP, TDX, HyperV... guests and whatever's
coming down the pipe. And all that goes into arch/x86/ kernel proper
code.

The CC_ATTR stuff is clean-ish in the sense that we have separation by
confidential computing platform - AMD's and Intel's. Hyper-V comes along
and wants to define a different subset of that. And that's only the
SEV-SNP side - there's a TDX patchset too.

And then some other hypervisor will come along and say, but but, I wanna
have X and Y and a pink pony too.

Oh, and there's this other fun with MTRRs where each HV decides to do
whatever it wants.

So, we have a zoo brewing on the horizon already!

If there's no clean definition of what each guest is and requires and
that stuff isn't documented properly and if depending on which "feature"
I need to check, I need to call a different function or query
a different variable, then it won't go anywhere as far as guest support
goes.

The cc_platform_has() thing gives us a relatively clean way to abstract
all those differences away and keep the code sane-ish.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette