Re: [PATCH v2 1/7] x86/boot: Remove verify_cpu() from secondary_startup_64()

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

On Mon, Jan 16, 2023 at 03:25:34PM +0100, Peter Zijlstra wrote:
> The boot trampolines from trampoline_64.S have code flow like:
> 
>   16bit BIOS                  SEV-ES                          64bit EFI
> 
>   trampoline_start()          sev_es_trampoline_start()       
> trampoline_start_64()
>     verify_cpu()                        |                             |
>   switch_to_protected:    <---------------'                           v
>        |                                                      
> pa_trampoline_compat()
>        v                                                              |
>   startup_32()                
> <-----------------------------------------------'
>        |
>        v
>   startup_64()
>        |
>        v
>   tr_start() := head_64.S:secondary_startup_64()
> 
> Since AP bringup always goes through the 16bit BIOS path (EFI doesn't
> touch the APs), there is already a verify_cpu() invocation.

So supposedly TDX/ACPI-6.4 comes in on trampoline_startup64() for APs --
can any of the TDX capable folks tell me if we need verify_cpu() on
these?

Aside from checking for LM, it seems to clear XD_DISABLE on Intel and
force enable SSE on AMD/K7. Surely none of that is needed for these
shiny new chips?

I mean, I can hack up a patch that adds verify_cpu() to the 64bit entry
point, but it seems really sad to need that on modern systems.