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

kirill.shutemov
2023-01-18T12:28:13Z

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