[PATCH 10/10] powerpc: move norestart trap flag to bit 0

[Christophe Leroy]

Le 15/03/2021 à 04:17, Nicholas Piggin a écrit :
> Compact the trap flags down to use the low 4 bits of regs.trap.
> 
> A few 64e interrupt trap numbers set bit 4. Although they tended to be
> trivial so it wasn't a real problem[1], it is not the right thing to do,
> and confusing.
> 
> [*] E.g., 0x310 hypercall goes to unknown_exception, which prints
>      regs->trap directly so 0x310 will appear fine, and only the syscall
>      interrupt will test norestart, so it won't be confused by 0x310.
> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>   arch/powerpc/include/asm/ptrace.h | 14 ++++++++++----
>   1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
> index 91194fdd5d01..6a04abfe5eb6 100644
> --- a/arch/powerpc/include/asm/ptrace.h
> +++ b/arch/powerpc/include/asm/ptrace.h
> @@ -185,15 +185,21 @@ static inline void regs_set_return_value(struct pt_regs *regs, unsigned long rc)
>   #define current_pt_regs() \
>   	((struct pt_regs *)((unsigned long)task_stack_page(current) + THREAD_SIZE) - 1)
>   
> +/*
> + * The 4 low bits (0xf) are available as flags to overload the trap word,
> + * because interrupt vectors have minimum alignment of 0x10. TRAP_FLAGS_MASK
> + * must cover the bits used as flags, including bit 0 which is used as the
> + * "norestart" bit.
> + */
>   #ifdef __powerpc64__
> -#define TRAP_FLAGS_MASK		0x10
> +#define TRAP_FLAGS_MASK		0x1
>   #define TRAP(regs)		((regs)->trap & ~TRAP_FLAGS_MASK)
>   #else
>   /*
>    * On 4xx we use bit 1 in the trap word to indicate whether the exception
>    * is a critical exception (1 means it is).
>    */
> -#define TRAP_FLAGS_MASK		0x1E
> +#define TRAP_FLAGS_MASK		0xf

Could we set 0xf for all and remove the ifdef __powerpc64__ ?

>   #define TRAP(regs)		((regs)->trap & ~TRAP_FLAGS_MASK)
>   #define IS_CRITICAL_EXC(regs)	(((regs)->trap & 2) != 0)
>   #define IS_MCHECK_EXC(regs)	(((regs)->trap & 4) != 0)
> @@ -222,12 +228,12 @@ static inline bool trap_is_syscall(struct pt_regs *regs)
>   
>   static inline bool trap_norestart(struct pt_regs *regs)
>   {
> -	return regs->trap & 0x10;
> +	return regs->trap & 0x1;
>   }
>   
>   static inline void set_trap_norestart(struct pt_regs *regs)
>   {
> -	regs->trap |= 0x10;
> +	regs->trap |= 0x1;
>   }
>   
>   #define arch_has_single_step()	(1)
> 

While we are playing with ->trap, in mm/book3s64/hash_utils.c there is an if (regs->trap == 0x400). 
Should be TRAP(regs) == 0x400 ?

Christophe