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

[kirill.shutemov@xxxxxxxxxxxxxxx]

On Wed, Jan 18, 2023 at 10:45:44AM +0100, Peter Zijlstra 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?

TDX has no XD_DISABLE set and it doesn't allow to write to
IA32_MISC_ENABLE MSR (triggers #VE), so we should be safe.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov