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

["H. Peter Anvin" <hpa@xxxxxxxxx>]

On January 18, 2023 1:45:44 AM PST, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>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.

Sad, perhaps, but really better for orthogonality – fewer special cases.