Re: [RFC v1 09/26] x86/tdx: Handle CPUID via #VE

[Andy Lutomirski]

On Mon, Feb 8, 2021 at 9:11 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> On Sun, Feb 07, 2021, Andy Lutomirski wrote:
> >

> > How much of the register state is revealed to the VMM when we do a TDVMCALL?
> > Presumably we should fully sanitize all register state that shows up in
> > cleartext on the other end, and we should treat all regs that can be modified
> > by the VMM as clobbered.
>
> The guest gets to choose, with a few restrictions.  RSP cannot be exposed to the
> host.  RAX, RCX, R10, and R11 are always exposed as they hold mandatory info
> about the TDVMCALL (TDCALL fn, GPR mask, GHCI vs. vendor, and TDVMCALL fn).  All
> other GPRs are exposed and clobbered if their bit in RCX is set, otherwise they
> are saved/restored by the TDX-Module.
>
> I agree with Dave, pass everything required by the GHCI in the main routine, and
> sanitize and save/restore all such GPRs.

Sounds okay to me.