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Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date:   Wed, 18 Oct 2023 12:20:15 +0200
From:   Ingo Molnar <mingo@kernel.org>
To:     Hou Wenlong <houwenlong.hwl@antgroup.com>
Cc:     linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "maintainer:X86 ARCHITECTURE 32-BIT AND 64-BIT" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Steve Rutherford <srutherford@google.com>,
        Michael Kelley <mikelley@microsoft.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH 2/2] x86/sme: Mark the code as __head in
 mem_encrypt_identity.c
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* Hou Wenlong <houwenlong.hwl@antgroup.com> wrote:

> On Tue, Oct 17, 2023 at 08:52:46PM +0800, Ingo Molnar wrote:
> > 
> > * Hou Wenlong <houwenlong.hwl@antgroup.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@antgroup.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.

The right solution at that point is to make <asm/init.h> self-contained...

> 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.

When exporting a localized definition you should consider namespace 
collisions - the name '__head' is way too generic, no wonder it caused 
problems elsewhere.

I'd suggest naming it __init_head or so, but still keep it in a x86-only 
header.

I presume keeping it all in the  separate section and widening its usage has a 
specific purpose? Please outline that in the changelog as well.

Ie. instead of mechanical patches that try to follow existing patterns 
cargo-cult style, this area of x86 code requires well-argued, well thought 
out patches that show background knowledge of the area.

Thanks,

	Ingo