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

[Nicholas Piggin <npiggin@gmail.com>]

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.

Thanks,
Nick