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SubjectRe: [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@gmail.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@gmail.com>
> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.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

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