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

Andy Lutomirski
2015-03-26T22:35:39Z

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
> */
> _
>