linux-kernel - Re: [PATCH 2/2] x86/sme: Mark the code as __head in mem_encrypt

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Message-ID: <20231018071347.GA87734@k08j02272.eu95sqa>
Date:   Wed, 18 Oct 2023 15:13:47 +0800
From:   "Hou Wenlong" <houwenlong.hwl@...group.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE 32-BIT AND 64-BIT" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steve Rutherford <srutherford@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 2/2] x86/sme: Mark the code as __head in
 mem_encrypt_identity.c

On Tue, Oct 17, 2023 at 08:52:46PM +0800, Ingo Molnar wrote:
> 
> * Hou Wenlong <houwenlong.hwl@...group.com> wrote:
> 
> > The functions sme_enable() and sme_encrypt_kernel() are only called by
> > the head code which runs in identity virtual address. Therefore, it's
> > better to mark them as __head as well.
> > 
> > Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
> > ---
> >  arch/x86/include/asm/mem_encrypt.h |  8 ++++----
> >  arch/x86/mm/mem_encrypt_identity.c | 27 ++++++++++++++-------------
> >  2 files changed, 18 insertions(+), 17 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> > index 359ada486fa9..48469e22a75e 100644
> > --- a/arch/x86/include/asm/mem_encrypt.h
> > +++ b/arch/x86/include/asm/mem_encrypt.h
> > @@ -46,8 +46,8 @@ void __init sme_unmap_bootdata(char *real_mode_data);
> >  
> >  void __init sme_early_init(void);
> >  
> > -void __init sme_encrypt_kernel(struct boot_params *bp);
> > -void __init sme_enable(struct boot_params *bp);
> > +void sme_encrypt_kernel(struct boot_params *bp);
> > +void sme_enable(struct boot_params *bp);
> >  
> >  int __init early_set_memory_decrypted(unsigned long vaddr, unsigned long size);
> >  int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size);
> > @@ -75,8 +75,8 @@ static inline void __init sme_unmap_bootdata(char *real_mode_data) { }
> >  
> >  static inline void __init sme_early_init(void) { }
> >  
> > -static inline void __init sme_encrypt_kernel(struct boot_params *bp) { }
> > -static inline void __init sme_enable(struct boot_params *bp) { }
> > +static inline void sme_encrypt_kernel(struct boot_params *bp) { }
> > +static inline void sme_enable(struct boot_params *bp) { }
> 
> So I think we should preserve the previous convention of marking functions 
> __init in the header-declaration and at the definition site as well, and do 
> the same with __head as well?
> 
Hi Ingo,

I tried to include <asm/init.h> into <asm/mem_encrypt.h> and mark the
function declaration as __head, but it resulted in a build failure. This
is because <asm/init.h> is not self-contained; the type "pgd_t" is
defined in <asm/pgtable_types.h>, which includes <asm/mem_encrypt.h>,
leading to mutual inclusion of header files. To avoid the issue of
complicated header file inclusion, I removed the annotation from the
function declaration.

Actually, initially, I noticed that the __init definition is in
<linux/init.h>, so I first placed the __head definition in
<linux/init.h> as well. However, this conflicted with the local variable
in the "list_next_or_null_rcu" macro in <linux/rculist.h>. Then I
realized that __head was only used in x86, so I made the decision to put
it in the architecture-specific header. Considering simplicity, I chose
to put the definition in <asm/init.h>. I also attempted to put the
definition in other headers such as <asm/boot.h> and
<asm/bootparam_utils.h>, and included them in <asm/mem_encrypt.h>, but
the build still failed.

Thanks!

> Thanks,
> 
> 	Ingo