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SubjectRe: [PATCH v2 1/4] x86/mm: surround level4_kernel_pgt with #ifdef CONFIG_X86_5LEVEL...#endif
On Sun, Oct 28, 2018 at 10:44:46AM +0900, Masahiro Yamada wrote:
> 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 ?
>
yes, I will update the commit msg.

>
> > 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;
> }
>
This is much better. I just declared it as 'inline'. Thanks for your suggestion.

>
>
>
> --
> Best Regards
> Masahiro Yamada

--
Thanks,
Changbin Du

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