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Date:   Wed, 18 Jan 2023 14:46:14 +0300
From:   kirill.shutemov@linux.intel.com
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     x86@kernel.org, Joan Bruguera <joanbrugueram@gmail.com>,
        linux-kernel@vger.kernel.org, Juergen Gross <jgross@suse.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        xen-devel <xen-devel@lists.xenproject.org>,
        Jan Beulich <jbeulich@suse.com>,
        Roger Pau Monne <roger.pau@citrix.com>,
        Kees Cook <keescook@chromium.org>, mark.rutland@arm.com,
        Andrew Cooper <Andrew.Cooper3@citrix.com>,
        =?utf-8?B?SsO2cmcgUsO2ZGVs?= <joro@8bytes.org>,
        "H. Peter Anvin" <hpa@zytor.com>, jroedel@suse.de,
        dave.hansen@intel.com, kai.huang@intel.com
Subject: Re: [PATCH v2 1/7] x86/boot: Remove verify_cpu() from
 secondary_startup_64()
Message-ID: <20230118114614.x2shsi6s3noiopux@box.shutemov.name>
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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