linux-kernel - Re: [PATCH v2 1/4] x86/mm: surround level4_kernel_pgt with #ifdef CONFIG_X86

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Message-ID: <CAK7LNAQJxVDWU5GPY4O6x+z_Pkmh4KuHiTpkY_LDJwNYO-eCBw@mail.gmail.com>
Date:   Sun, 28 Oct 2018 10:44:46 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     changbin.du@...il.com
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>, X86 ML <x86@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-sparse@...r.kernel.org, Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v2 1/4] x86/mm: surround level4_kernel_pgt with #ifdef CONFIG_X86_5LEVEL...#endif

On Fri, Oct 19, 2018 at 9:50 PM Du Changbin <changbin.du@...il.com> wrote:
>
> The level4_kernel_pgt is only defined when X86_5LEVEL is enabled. So
> surround level4_kernel_pgt with #ifdef CONFIG_X86_5LEVEL...#endif to
> make code correct.

For clarification, is it better to mention
that this is a preparation for CONFIG_CC_OPTIMIZE_FOR_DEBUGGING ?


> Signed-off-by: Du Changbin <changbin.du@...il.com>
> Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
>  arch/x86/include/asm/pgtable_64.h |  2 ++
>  arch/x86/kernel/head64.c          | 13 ++++++-------
>  2 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
> index 9c85b54bf03c..9333f7fa5bdb 100644
> --- a/arch/x86/include/asm/pgtable_64.h
> +++ b/arch/x86/include/asm/pgtable_64.h
> @@ -16,7 +16,9 @@
>  #include <linux/threads.h>
>  #include <asm/fixmap.h>
>
> +#ifdef CONFIG_X86_5LEVEL
>  extern p4d_t level4_kernel_pgt[512];
> +#endif


Is this #ifdef  necessary?

It is harmless to declaring unused stuff.



>  extern p4d_t level4_ident_pgt[512];
>  extern pud_t level3_kernel_pgt[512];
>  extern pud_t level3_ident_pgt[512];
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index ddee1f0870c4..4a59ef93c258 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -151,16 +151,15 @@ unsigned long __head __startup_64(unsigned long physaddr,
>
>         pgd = fixup_pointer(&early_top_pgt, physaddr);
>         p = pgd + pgd_index(__START_KERNEL_map);
> -       if (la57)
> -               *p = (unsigned long)level4_kernel_pgt;
> -       else
> -               *p = (unsigned long)level3_kernel_pgt;
> -       *p += _PAGE_TABLE_NOENC - __START_KERNEL_map + load_delta;
> -
> +#ifdef CONFIG_X86_5LEVEL
>         if (la57) {
> +               *p = (unsigned long)level4_kernel_pgt;
>                 p4d = fixup_pointer(&level4_kernel_pgt, physaddr);
>                 p4d[511] += load_delta;
> -       }
> +       } else
> +#endif
> +               *p = (unsigned long)level3_kernel_pgt;
> +       *p += _PAGE_TABLE_NOENC - __START_KERNEL_map + load_delta;
>
>         pud = fixup_pointer(&level3_kernel_pgt, physaddr);
>         pud[510] += load_delta;
> --
> 2.17.1
>


Hmm, this code looks a bit ugly...

Does the following one liner work with CONFIG_CC_OPTIMIZE_FOR_DEBUGGING ?


diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 8047379..579847f 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -97,7 +97,7 @@ static bool __head check_la57_support(unsigned long physaddr)
        return true;
 }
 #else
-static bool __head check_la57_support(unsigned long physaddr)
+static __always_inline bool __head check_la57_support(unsigned long physaddr)
 {
        return false;
 }




--
Best Regards
Masahiro Yamada