[PATCH v2 2/2] arm64: Fix single stepping in kernel traps

[Julien Thierry]

On 11/10/17 15:37, Will Deacon wrote:
> On Wed, Oct 11, 2017 at 02:48:41PM +0100, Julien Thierry wrote:
>> Software Step exception is missing after stepping a trapped instruction.
>>
>> Ensure SPSR.SS gets set to 0 after emulating/skipping a trapped instruction
>> before doing ERET.
>>
>> Signed-off-by: Julien Thierry <julien.thierry at arm.com>
>> Reviewed-by: Alex Bennée <alex.bennee at linaro.org>
>> Cc: Catalin Marinas <catalin.marinas at arm.com>
>> Cc: Will Deacon <will.deacon at arm.com>
>> Cc: Mark Rutland <mark.rutland at arm.com>
>>
>> ---
>>   arch/arm64/include/asm/insn.h        |  5 +++++
>>   arch/arm64/include/asm/traps.h       |  6 ++++++
>>   arch/arm64/kernel/armv8_deprecated.c |  8 ++++----
>>   arch/arm64/kernel/cpufeature.c       |  2 +-
>>   arch/arm64/kernel/traps.c            | 21 ++++++++++++++++-----
>>   5 files changed, 32 insertions(+), 10 deletions(-)
> 
> [...]
> 
>> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
>> index 5ea4b85..aaf9a523 100644
>> --- a/arch/arm64/kernel/traps.c
>> +++ b/arch/arm64/kernel/traps.c
>> @@ -293,6 +293,17 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
>>   	}
>>   }
>>
>> +void arm64_setup_next_instr(struct pt_regs *regs, unsigned long size)
>> +{
>> +	regs->pc += size;
>> +
>> +	/*
>> +	 * If we were single stepping, we want to get the step exception after
>> +	 * we return from the trap.
>> +	 */
>> +	regs->pstate &= ~DBG_SPSR_SS;
> 
> Can you use user_fastforward_single_step instead, like we do for the signal
> handling path?

I guess we are always fast forwarding on the current task. So yes, I can 
use that.

Thanks,

-- 
Julien Thierry