[PATCH v10 2/2] powerpc/64s: KVM update for reimplement book3s idle code in C

[Nicholas Piggin]

Paul Mackerras's on May 13, 2019 4:42 pm:
> On Sun, Apr 28, 2019 at 09:45:15PM +1000, Nicholas Piggin wrote:
>> This is the KVM update to the new idle code. A few improvements:
>> 
>> - Idle sleepers now always return to caller rather than branch out
>>   to KVM first.
>> - This allows optimisations like very fast return to caller when no
>>   state has been lost.
>> - KVM no longer requires nap_state_lost because it controls NVGPR
>>   save/restore itself on the way in and out.
>> - The heavy idle wakeup KVM request check can be moved out of the
>>   normal host idle code and into the not-performance-critical offline
>>   code.
>> - KVM nap code now returns from where it is called, which makes the
>>   flow a bit easier to follow.
> 
> One question below...
> 
>> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> index 58d0f1ba845d..f66191d8f841 100644
>> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> ...
>> @@ -2656,6 +2662,9 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
>>  
>>  	lis	r3, LPCR_PECEDP at h	/* Do wake on privileged doorbell */
>>  
>> +	/* Go back to host stack */
>> +	ld	r1, HSTATE_HOST_R1(r13)
> 
> At this point we are in kvmppc_h_cede, which we branched to from
> hcall_try_real_mode, which came from the guest exit path, where we
> have already loaded r1 from HSTATE_HOST_R1(r13).  So if there is a
> path to get here with r1 not already set to HSTATE_HOST_R1(r13), then
> I missed it - please point it out to me.  Otherwise this statement
> seems superfluous.

I'm not sure why I put that there. I think you're right it could
be removed.

Thanks,
Nick