Subject: Re: [2/2] powerpc/smp: Add smp_muxed_ipi_rm_message_pass

From: "Suresh E. Warrier" <[email-masked]>
Date: Mon, 16 Nov 2015 15:34:48 -0600

Hi Mike,

The changes you proposed look nicer than what I have here.
I will get that coded and tested and re=submit.

Thanks.
-suresh

On 11/15/2015 11:53 PM, Michael Ellerman wrote:
> Hi Suresh,
> 
> On Thu, 2015-29-10 at 23:40:45 UTC, "Suresh E. Warrier" wrote:
>> This function supports IPI message passing for real
>> mode callers.
>>
>> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
>> index a53a130..8c07bfad 100644
>> --- a/arch/powerpc/kernel/smp.c
>> +++ b/arch/powerpc/kernel/smp.c
>> @@ -235,6 +238,33 @@ void smp_muxed_ipi_message_pass(int cpu, int msg)
>>  	smp_ops->cause_ipi(cpu, info->data);
>>  }
>>  
>> +#if defined(CONFIG_KVM_XICS) && defined(CONFIG_KVM_BOOK3S_HV_POSSIBLE)
>> +/*
>> + * Message passing code for real mode callers. It does not use the
>> + * smp_ops->cause_ipi function to cause an IPI, because those functions
>> + * access the MFFR through an ioremapped address.
>> + */
>> +void smp_muxed_ipi_rm_message_pass(int cpu, int msg)
>> +{
>> +	struct cpu_messages *info = &per_cpu(ipi_message, cpu);
>> +	char *message = (char *)&info->messages;
>> +	unsigned long xics_phys;
>> +
>> +	/*
>> +	 * Order previous accesses before accesses in the IPI handler.
>> +	 */
>> +	smp_mb();
>> +	message[msg] = 1;
>> +
>> +	/*
>> +	 * cause_ipi functions are required to include a full barrier
>> +	 * before doing whatever causes the IPI.
>> +	 */
>> +	xics_phys = paca[cpu].kvm_hstate.xics_phys;
>> +	out_rm8((u8 *)(xics_phys + XICS_MFRR), IPI_PRIORITY);
>> +}
>> +#endif
> 
> 
> I'm not all that happy with this. This function does two things, one of which
> belongs in this file (setting message), and the other which definitely does
> not (the XICs part).
> 
> I think the end result would be cleaner if we did something like:
> 
> void smp_muxed_ipi_set_message(int cpu, int msg)
> {
> 	struct cpu_messages *info = &per_cpu(ipi_message, cpu);
> 	char *message = (char *)&info->messages;
> 	unsigned long xics_phys;
> 
> 	/*
> 	 * Order previous accesses before accesses in the IPI handler.
> 	 */
> 	smp_mb();
> 	message[msg] = 1;
> }
> 
> Which would be exported, and could also be used by smp_muxed_ipi_message_pass().
> 
> Then in icp_rm_set_vcpu_irq(), you would do something like:
> 
> 	if (hcore != -1) {
> 		hcpu = hcore << threads_shift;
> 		kvmppc_host_rm_ops_hv->rm_core[hcore].rm_data = vcpu;
> 		smp_muxed_ipi_set_message(hcpu, PPC_MSG_RM_HOST_ACTION);
> 		icp_native_cause_ipi_real_mode();
> 	}
> 
> Where icp_native_cause_ipi_real_mode() is a new hook you define in icp_native.c
> which does the real mode write to MFRR.
> 
> cheers
>