Re: [PATCH 09/17] x86: make is_64bit_mm() widely available

[Andy Lutomirski <luto@kernel.org>]

On 03/26/2015 11:33 AM, Dave Hansen wrote:
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> The uprobes code has a nice helper, is_64bit_mm(), that consults both
> the runtime and compile-time flags for 32-bit support.  Instead of
> reinventing the wheel, pull it in to an x86 header so we can use it
> for MPX.
>
> I prefer passing the mm around to test_thread_flag(TIF_IA32) beacuse
> it makes it explicit where the context is coming from.  It will also
> make it easier if we ever need to access the MPX structures from
> another process.
>
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Oleg Nesterov <oleg@redhat.com>

I like this.  Maybe we can remove TIF_IA32 entirely at some point based 
on this :)

> ---
>
>   b/arch/x86/include/asm/mmu_context.h |   13 +++++++++++++
>   b/arch/x86/kernel/uprobes.c          |   10 +---------
>   2 files changed, 14 insertions(+), 9 deletions(-)
>
> diff -puN arch/x86/include/asm/mmu_context.h~x86-make-is_64bit_mm-available arch/x86/include/asm/mmu_context.h
> --- a/arch/x86/include/asm/mmu_context.h~x86-make-is_64bit_mm-available	2015-03-26 11:27:31.685419698 -0700
> +++ b/arch/x86/include/asm/mmu_context.h	2015-03-26 11:27:31.690419923 -0700
> @@ -142,6 +142,19 @@ static inline void arch_exit_mmap(struct
>   	paravirt_arch_exit_mmap(mm);
>   }
>
> +#ifdef CONFIG_X86_64
> +static inline bool is_64bit_mm(struct mm_struct *mm)
> +{
> +	return	!config_enabled(CONFIG_IA32_EMULATION) ||
> +		!(mm->context.ia32_compat == TIF_IA32);
> +}
> +#else
> +static inline bool is_64bit_mm(struct mm_struct *mm)
> +{
> +	return false;
> +}
> +#endif
> +
>   static inline void arch_bprm_mm_init(struct mm_struct *mm,
>   		struct vm_area_struct *vma)
>   {
> diff -puN arch/x86/kernel/uprobes.c~x86-make-is_64bit_mm-available arch/x86/kernel/uprobes.c
> --- a/arch/x86/kernel/uprobes.c~x86-make-is_64bit_mm-available	2015-03-26 11:27:31.687419788 -0700
> +++ b/arch/x86/kernel/uprobes.c	2015-03-26 11:27:31.690419923 -0700
> @@ -29,6 +29,7 @@
>   #include <linux/kdebug.h>
>   #include <asm/processor.h>
>   #include <asm/insn.h>
> +#include <asm/mmu_context.h>
>
>   /* Post-execution fixups. */
>
> @@ -312,11 +313,6 @@ static int uprobe_init_insn(struct arch_
>   }
>
>   #ifdef CONFIG_X86_64
> -static inline bool is_64bit_mm(struct mm_struct *mm)
> -{
> -	return	!config_enabled(CONFIG_IA32_EMULATION) ||
> -		!(mm->context.ia32_compat == TIF_IA32);
> -}
>   /*
>    * If arch_uprobe->insn doesn't use rip-relative addressing, return
>    * immediately.  Otherwise, rewrite the instruction so that it accesses
> @@ -497,10 +493,6 @@ static void riprel_post_xol(struct arch_
>   	}
>   }
>   #else /* 32-bit: */
> -static inline bool is_64bit_mm(struct mm_struct *mm)
> -{
> -	return false;
> -}
>   /*
>    * No RIP-relative addressing on 32-bit
>    */
> _
>