Re: [PATCH] arm64: entry: dedup SDEI event priority selection

[Bradley Morgan]

On July 21, 2026 3:50:12 PM GMT+01:00, Mark Rutland <mark.rutland@xxxxxxx>
wrote:
>On Sat, Jul 18, 2026 at 06:54:47PM +0000, Bradley Morgan wrote:
>> __sdei_asm_handler open codes the same branch ladder four times to pick
>> the normal or critical variant of a per CPU variable based on the SDEI
>> event priority: when recording the active event, when selecting the
>> SDEI stack, when selecting the shadow call stack, and when clearing the
>> active-event record on exit.
>> 
>> Add a sdei_choose macro, using \@ local labels like the files existing
>> macros, and replace the four open coded copies with it. This also drops
>> the repeated reuse of the 1:/2:/3:/4: numeric labels in this handler.
>> 
>> No functional change intended.
>> 
>> Signed-off-by: Bradley Morgan <include@xxxxxxxxx>
>> ---
>>  arch/arm64/kernel/entry.S | 39 +++++++++++++++++++--------------------
>>  1 file changed, 19 insertions(+), 20 deletions(-)
>
>Looking at the patch below, the result is far less readable, and this
>has only saved a single line.
>
>I don't think this is worthwhile; please leave this as-is.
>
>Mark.

ok, fair enough, I wasn't highly expecting for this to get accepted,
the one I think that would, would be [1]

[1] https://lore.kernel.org/all/20260717114746.15109-1-include@xxxxxxxxx/

Thanks for the review.

>> 
>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
>> index e0db14e9c843..29ef4a0d28a8 100644
>> --- a/arch/arm64/kernel/entry.S
>> +++ b/arch/arm64/kernel/entry.S
>> @@ -916,6 +916,15 @@ NOKPROBE(call_on_irq_stack)
>>  	b	.
>>  .endm
>>  
>> +/* Set \dst using \op and the \normal or \critical sym, based on \prio
>*/
>> +.macro sdei_choose op:req, dst:req, prio:req, normal:req, critical:req,
>tmp:req
>> +	cbnz	\prio, .Lcritical\@
>> +	\op dst=\dst, sym=\normal, tmp=\tmp
>> +	b	.Ldone\@
>> +.Lcritical\@:	\op dst=\dst, sym=\critical, tmp=\tmp
>> +.Ldone\@:
>> +.endm
>> +
>>  #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
>>  /*
>>   * The regular SDEI entry point may have been unmapped along with the
>rest of
>> @@ -997,32 +1006,24 @@ SYM_CODE_START(__sdei_asm_handler)
>>  
>>  	/* Store the registered-event for crash_smp_send_stop() */
>>  	ldrb	w4, [x19, #SDEI_EVENT_PRIORITY]
>> -	cbnz	w4, 1f
>> -	adr_this_cpu dst=x5, sym=sdei_active_normal_event, tmp=x6
>> -	b	2f
>> -1:	adr_this_cpu dst=x5, sym=sdei_active_critical_event, tmp=x6
>> -2:	str	x19, [x5]
>> +	sdei_choose adr_this_cpu, x5, w4, sdei_active_normal_event, \
>> +		    sdei_active_critical_event, x6
>> +	str	x19, [x5]
>>  
>>  	/*
>>  	 * entry.S may have been using sp as a scratch register, find whether
>>  	 * this is a normal or critical event and switch to the appropriate
>>  	 * stack for this CPU.
>>  	 */
>> -	cbnz	w4, 1f
>> -	ldr_this_cpu dst=x5, sym=sdei_stack_normal_ptr, tmp=x6
>> -	b	2f
>> -1:	ldr_this_cpu dst=x5, sym=sdei_stack_critical_ptr, tmp=x6
>> -2:	mov	x6, #SDEI_STACK_SIZE
>> +	sdei_choose ldr_this_cpu, x5, w4, sdei_stack_normal_ptr, sdei_stack_critical_ptr, x6
>> +	mov	x6, #SDEI_STACK_SIZE
>>  	add	x5, x5, x6
>>  	mov	sp, x5
>>  
>>  #ifdef CONFIG_SHADOW_CALL_STACK
>>  	/* Use a separate shadow call stack for normal and critical events */
>> -	cbnz	w4, 3f
>> -	ldr_this_cpu dst=scs_sp, sym=sdei_shadow_call_stack_normal_ptr, tmp=x6
>> -	b	4f
>> -3:	ldr_this_cpu dst=scs_sp, sym=sdei_shadow_call_stack_critical_ptr, tmp=x6
>> -4:
>> +	sdei_choose ldr_this_cpu, scs_sp, w4, sdei_shadow_call_stack_normal_ptr, \
>> +		    sdei_shadow_call_stack_critical_ptr, x6
>>  #endif
>>  
>>  	/*
>> @@ -1068,11 +1069,9 @@ SYM_CODE_START(__sdei_asm_handler)
>>  
>>  	/* Clear the registered-event seen by crash_smp_send_stop() */
>>  	ldrb	w3, [x4, #SDEI_EVENT_PRIORITY]
>> -	cbnz	w3, 1f
>> -	adr_this_cpu dst=x5, sym=sdei_active_normal_event, tmp=x6
>> -	b	2f
>> -1:	adr_this_cpu dst=x5, sym=sdei_active_critical_event, tmp=x6
>> -2:	str	xzr, [x5]
>> +	sdei_choose adr_this_cpu, x5, w3, sdei_active_normal_event, \
>> +		    sdei_active_critical_event, x6
>> +	str	xzr, [x5]
>>  
>>  alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0
>>  	sdei_handler_exit exit_mode=x2
>> -- 
>> 2.53.0
>> 
>> 
>

Thanks!