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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Mon, 10 Jul 2023 23:55:49 +0200
Message-ID: <CAMj1kXGUtm2unrpwLWCXQhoE1wEYuFgvz3u_SXDFE=SJHJdYmQ@mail.gmail.com>
Subject: Re: [PATCH v5 06/20] x86/decompressor: Store boot_params pointer in
 callee save register
To:     Borislav Petkov <bp@alien8.de>
Cc:     linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
        Evgeniy Baskov <baskov@ispras.ru>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Alexey Khoroshilov <khoroshilov@ispras.ru>,
        Peter Jones <pjones@redhat.com>,
        Gerd Hoffmann <kraxel@redhat.com>,
        Dave Young <dyoung@redhat.com>,
        Mario Limonciello <mario.limonciello@amd.com>,
        Kees Cook <keescook@chromium.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Joerg Roedel <jroedel@suse.de>
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On Mon, 10 Jul 2023 at 11:07, Borislav Petkov <bp@alien8.de> wrote:
>
> On Wed, Jun 07, 2023 at 09:23:28AM +0200, Ard Biesheuvel wrote:
> > Instead of pushing and popping %RSI several times to preserve the struct
> > boot_params pointer across the execution of the startup code, move it
> > into a callee save register before the first call into C, and copy it
> > back when needed.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> >  arch/x86/boot/compressed/head_64.S | 34 +++++++-------------
> >  1 file changed, 11 insertions(+), 23 deletions(-)
>
> I like that.
>
> We do a similar dance in arch/x86/kernel/head_64.S. Care to fix that
> too, in a separate patch?
>

I already did, actually, but I dropped it from this series because it
was getting too long, and not essential for the overall goal of the
changes.

https://lore.kernel.org/all/20230602101313.3557775-19-ardb@kernel.org/