linux-kernel - Re: [PATCH v5 10/20] x86/decompressor: Call trampoline directly from C code

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Message-ID: <20230608181540.GA2469@yjiang5-mobl.amr.corp.intel.com>
Date:   Thu, 8 Jun 2023 11:15:40 -0700
From:   Yunhong Jiang <yunhong.jiang@...ux.intel.com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Evgeniy Baskov <baskov@...ras.ru>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        Peter Jones <pjones@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Dave Young <dyoung@...hat.com>,
        Mario Limonciello <mario.limonciello@....com>,
        Kees Cook <keescook@...omium.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH v5 10/20] x86/decompressor: Call trampoline directly from
 C code

On Thu, Jun 08, 2023 at 10:04:43AM +0200, Ard Biesheuvel wrote:
> On Wed, 7 Jun 2023 at 20:09, Yunhong Jiang
> <yunhong.jiang@...ux.intel.com> wrote:
> >
> > On Wed, Jun 07, 2023 at 09:23:32AM +0200, Ard Biesheuvel wrote:
> > > Instead of returning to the asm calling code to invoke the trampoline,
> > > call it straight from the C code that sets the scene. That way, the
> > > struct return type is no longer needed for returning two values, and the
> > > call can be made conditional more cleanly in a subsequent patch.
> > >
> > > Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > > Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> > > ---
> > >  arch/x86/boot/compressed/head_64.S    | 20 +++-----------
> > >  arch/x86/boot/compressed/pgtable_64.c | 28 ++++++++------------
> > >  2 files changed, 15 insertions(+), 33 deletions(-)
> > >
> ...
> > > diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
> > > index d66639c961b8eeda..1d28ad95ea839531 100644
> > > --- a/arch/x86/boot/compressed/pgtable_64.c
> > > +++ b/arch/x86/boot/compressed/pgtable_64.c
> > > @@ -16,11 +16,6 @@ unsigned int __section(".data") pgdir_shift = 39;
> > >  unsigned int __section(".data") ptrs_per_p4d = 1;
> > >  #endif
> > >
> > > -struct paging_config {
> > > -     unsigned long trampoline_start;
> > > -     unsigned long l5_required;
> > > -};
> > > -
> > >  /* Buffer to preserve trampoline memory */
> > >  static char trampoline_save[TRAMPOLINE_32BIT_SIZE];
> > >
> > > @@ -106,10 +101,10 @@ static unsigned long find_trampoline_placement(void)
> > >       return bios_start - TRAMPOLINE_32BIT_SIZE;
> > >  }
> > >
> > > -struct paging_config paging_prepare(void *rmode)
> > > +asmlinkage void set_paging_levels(void *rmode)
> >
> > Can you please change the refer to paging_prepare() in the comments above also?
> 
> You mean the below, right?
> 
> --- a/arch/x86/boot/compressed/pgtable_64.c
> +++ b/arch/x86/boot/compressed/pgtable_64.c
> @@ -24,7 +24,7 @@ static char trampoline_save[TRAMPOLINE_32BIT_SIZE];
>   * purposes.
>   *
>   * Avoid putting the pointer into .bss as it will be cleared between
> - * paging_prepare() and extract_kernel().
> + * set_paging_levels() and extract_kernel().
>   */
>  unsigned long *trampoline_32bit __section(".data");

Yes.