linux-kernel - Re: [PATCH v2 1/7] x86/boot: Remove verify_cpu() from secondary_startup

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Message-ID: <Y8ZppgQ3RyzcR8eJ@gmail.com>
Date:   Tue, 17 Jan 2023 10:25:58 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, Joan Bruguera <joanbrugueram@...il.com>,
        linux-kernel@...r.kernel.org, Juergen Gross <jgross@...e.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Jan Beulich <jbeulich@...e.com>,
        Roger Pau Monne <roger.pau@...rix.com>,
        Kees Cook <keescook@...omium.org>, mark.rutland@....com,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Jörg Rödel <joro@...tes.org>,
        "H. Peter Anvin" <hpa@...or.com>, jroedel@...e.de
Subject: Re: [PATCH v2 1/7] x86/boot: Remove verify_cpu() from
 secondary_startup_64()


* Peter Zijlstra <peterz@...radead.org> 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()

oh ... this nice flow chart should move into a prominent C comment I think, 
it's far too good to be forgotten in an Git commit changelog.

> Since AP bringup always goes through the 16bit BIOS path (EFI doesn't
> touch the APs), there is already a verify_cpu() invocation.
> 
> Removing the verify_cpu() invocation from secondary_startup_64()
> renders the whole secondary_startup_64_no_verify() thing moot, so
> remove that too.
> 
> Cc: jroedel@...e.de
> Cc: hpa@...or.com
> Fixes: e81dc127ef69 ("x86/callthunks: Add call patching for call depth tracking")
> Reported-by: Joan Bruguera <joanbrugueram@...il.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Reviewed-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo