Re: [PATCH v8 01/40] x86/compressed/64: detect/setup SEV/SME features earlier in boot

Venu Busireddy
2021-12-15T18:18:44Z

On 2021-12-15 11:49:34 -0600, Michael Roth wrote:
>
> I think in the greater context of consolidating all the SME/SEV setup
> and re-using code, this helper stands a high chance of eventually becoming
> something more along the lines of sme_sev_parse_cpuid(), since otherwise
> we'd end up re-introducing multiple helpers to parse the same 0x8000001F
> fields if we ever need to process any of the other fields advertised in
> there. Given that, it makes sense to reserve the return value as an
> indication that either SEV or SME are enabled, and then have a
> pass-by-pointer parameters list to collect the individual feature
> bits/encryption mask for cases where SEV/SME are enabled, which are only
> treated as valid if sme_sev_parse_cpuid() returns 0.
>
> So Venu's original approach of passing the encryption mask by pointer
> seems a little closer toward that end, but I also agree Tom's approach
> is cleaner for the current code base, so I'm fine either way, just
> figured I'd mention this.
>
> I think needing to pass in the SME/SEV CPUID bits to tell the helper when
> to parse encryption bit and when not to is a little bit awkward though.
> If there's some agreement that this will ultimately serve the purpose of
> handling all (or most) of SME/SEV-related CPUID parsing, then the caller
> shouldn't really need to be aware of any individual bit positions.
> Maybe a bool could handle that instead, e.g.:
>
> int get_me_bit(bool sev_only, ...)
>
> or
>
> int sme_sev_parse_cpuid(bool sev_only, ...)
>
> where for boot/compressed sev_only=true, for kernel proper sev_only=false.

I can implement it this way too. But I am wondering if having a
boolean argument limits us from handling any future additions to the
bit positions.

Boris & Tom, which implementation would you prefer?

Venu