[PATCHv4 1/3] powerpc, cpu: partially unbind the mapping between cpu logical id and its seq in dt

[Benjamin Herrenschmidt]

On Mon, 2018-03-12 at 12:43 +0800, Pingfan Liu wrote:
> For kexec -p, the boot cpu can be not the cpu0, this causes the problem
> to alloc paca[]. In theory, there is no requirement to assign cpu's logical
> id as its present seq by device tree. But we have something like
> cpu_first_thread_sibling(), which makes assumption on the mapping inside
> a core. Hence partially changing the mapping, i.e. unbind the mapping of
> core while keep the mapping inside a core. After this patch, boot-cpu
> will always be mapped into the range [0,threads_per_core).

I'm ok with the idea but not fan of the implementation:

> Signed-off-by: Pingfan Liu <kernelfans at gmail.com>
> ---
>  arch/powerpc/include/asm/smp.h     |  1 +
>  arch/powerpc/kernel/prom.c         | 25 ++++++++++++++-----------
>  arch/powerpc/kernel/setup-common.c | 21 +++++++++++++++++++++
>  3 files changed, 36 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
> index fac963e..1299100 100644
> --- a/arch/powerpc/include/asm/smp.h
> +++ b/arch/powerpc/include/asm/smp.h
> @@ -30,6 +30,7 @@
>  #include <asm/percpu.h>
>  
>  extern int boot_cpuid;
> +extern int boot_cpuhwid;
>  extern int spinning_secondaries;
>  
>  extern void cpu_die(void);
> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> index da67606..d0ebb25 100644
> --- a/arch/powerpc/kernel/prom.c
> +++ b/arch/powerpc/kernel/prom.c
> @@ -315,8 +315,7 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
>  	const __be32 *intserv;
>  	int i, nthreads;
>  	int len;
> -	int found = -1;
> -	int found_thread = 0;
> +	bool found = false;
>  
>  	/* We are scanning "cpu" nodes only */
>  	if (type == NULL || strcmp(type, "cpu") != 0)
> @@ -341,8 +340,11 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
>  		if (fdt_version(initial_boot_params) >= 2) {
>  			if (be32_to_cpu(intserv[i]) ==
>  			    fdt_boot_cpuid_phys(initial_boot_params)) {
> -				found = boot_cpu_count;
> -				found_thread = i;
> +				/* always map the boot-cpu logical id into the
> +				 * the range of [0, thread_per_core)
> +				 */
> +				boot_cpuid = i;
> +				found = true;
>  			}

Call it boot_thread_id

>  		} else {
>  			/*
> @@ -351,8 +353,10 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
>  			 * off secondary threads.
>  			 */
>  			if (of_get_flat_dt_prop(node,
> -					"linux,boot-cpu", NULL) != NULL)
> -				found = boot_cpu_count;
> +					"linux,boot-cpu", NULL) != NULL) {
> +				boot_cpuid = i;
> +				found = true;
> +			}
>  		}
>  #ifdef CONFIG_SMP
>  		/* logical cpu id is always 0 on UP kernels */
> @@ -361,13 +365,12 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
>  	}
>  
>  	/* Not the boot CPU */
> -	if (found < 0)
> +	if (!found)
>  		return 0;
>  
> -	DBG("boot cpu: logical %d physical %d\n", found,
> -	    be32_to_cpu(intserv[found_thread]));
> -	boot_cpuid = found;
> -	set_hard_smp_processor_id(found, be32_to_cpu(intserv[found_thread]));
> +	boot_cpuhwid = be32_to_cpu(intserv[boot_cpuid]);
> +	DBG("boot cpu: logical %d physical %d\n", boot_cpuid, boot_cpuhwid);
> +	set_hard_smp_processor_id(boot_cpuid, boot_cpuhwid);
>  
>  	/*
>  	 * PAPR defines "logical" PVR values for cpus that
> diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
> index 66f7cc6..1a67344 100644
> --- a/arch/powerpc/kernel/setup-common.c
> +++ b/arch/powerpc/kernel/setup-common.c
> @@ -86,6 +86,7 @@ struct machdep_calls *machine_id;
>  EXPORT_SYMBOL(machine_id);
>  
>  int boot_cpuid = -1;
> +int boot_cpuhwid = -1;
>  EXPORT_SYMBOL_GPL(boot_cpuid);
>  
>  /*
> @@ -459,11 +460,17 @@ static void __init cpu_init_thread_core_maps(int tpc)
>  void __init smp_setup_cpu_maps(void)
>  {
>  	struct device_node *dn;
> +	struct device_node *boot_dn = NULL;
> +	bool handling_bootdn = true;
>  	int cpu = 0;
>  	int nthreads = 1;
>  
>  	DBG("smp_setup_cpu_maps()\n");
>  
> +again:
> +	/* E.g. kexec will not boot from the 1st core. So firstly loop to find out
> +	 * the dn of boot-cpu, and map them onto [0, nthreads)
> +	 */
>  	for_each_node_by_type(dn, "cpu") {
>  		const __be32 *intserv;
>  		__be32 cpu_be;
> @@ -488,6 +495,16 @@ void __init smp_setup_cpu_maps(void)
>  
>  		nthreads = len / sizeof(int);
>  
> +		if (handling_bootdn) {
> +			if (boot_cpuid < nthreads &&
> +				be32_to_cpu(intserv[boot_cpuid]) == boot_cpuhwid) {
> +				boot_dn = dn;
> +			}
> +			if (boot_dn == NULL)
> +				continue;
> +		} else if (dn == boot_dn)
> +			continue;
> +
>  		for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
>  			bool avail;
>  
> @@ -509,6 +526,10 @@ void __init smp_setup_cpu_maps(void)
>  			of_node_put(dn);
>  			break;
>  		}
> +		if (handling_bootdn) {
> +			handling_bootdn = false;
> +			goto again;
> +		}
>  	}

You don't need that "again" loop and "handling_bootdn" weird boolean.

Instead, start with cpu = 1 instead of cpu = 0, and rename it to
"next_cpu".

Then, before the thread loop, check if we are on the same core
as boot_cpuhwid:

	if (same_core_as_boot_cpu(intserv)) {
		cpu = 0;
	} else if (next_cpu < nr_cpus_ids) {
		cpu = next_cpu++;
	} else {
		of_node_put(dn);
		break;
	}

>  
>  	/* If no SMT supported, nthreads is forced to 1 */