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

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