[2/2] powerpc/smp: Add smp_muxed_ipi_rm_message_pass

[Michael Ellerman]

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