linux-kernel - Re: [PATCHv2 16/29] x86/boot: Add a trampoline for booting APs via firmware handoff

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Message-ID: <20220215213624.tzdahmbhucupwtqe@black.fi.intel.com>
Date:   Wed, 16 Feb 2022 00:36:24 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        tglx@...utronix.de, mingo@...hat.com, dave.hansen@...el.com,
        luto@...nel.org, peterz@...radead.org, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        Kai Huang <kai.huang@...el.com>
Subject: Re: [PATCHv2 16/29] x86/boot: Add a trampoline for booting APs via
 firmware handoff

On Fri, Feb 04, 2022 at 02:49:59PM +0100, Borislav Petkov wrote:
> On Fri, Feb 04, 2022 at 03:27:19AM -0800, Kuppuswamy, Sathyanarayanan wrote:
> > trampoline_start and sev_es_trampoline_start are not mutually exclusive.
> > Both are
> > used in arch/x86/kernel/sev.c.
> 
> I know - I've asked Jörg to have a look here.
> 
> > But trampoline_start64 can be removed and replaced with trampoline_start.
> > But using
> > _*64 suffix makes it clear that is used for 64 bit(CONFIG_X86_64).
> > 
> > Adding it for clarity seems to be fine to me.
> 
> Does it matter if the start IP is the same for all APs? Or do will there
> be a case where you have some APs starting from the 32-bit trampoline
> and some from the 64-bit one, on the same system? (that would be weird
> but what do I know...)

I'm not sure I follow. SMP bring up is new topic for me.

We want a single kernel binary that boots everywhere, so we cannot know at
build time if a secondary CPU will start in 32- or 64-bit mode.

How can signle trampoline_start cover all cases?

-- 
 Kirill A. Shutemov