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

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 16/03/2021 à 08:11, Nicholas Piggin a écrit :
> Excerpts from Christophe Leroy's message of March 15, 2021 6:14 pm:
>>
>>
>> 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@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__ ?
> 
> I like that it documents the bit number allocation so I prefer to leave
> it, but TRAP() does not have to be defined twice at least.
> 
>>
>>>    #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 ?
> 
> Yes I would say so, if you want to do a patch you can add
> Acked-by: Nicholas Piggin <npiggin@gmail.com>
> 
> Otherwise I can do it.

Yes please do.

Thanks
Christophe