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

[Pingfan Liu]

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).

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;
 			}
 		} 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;
+		}
 	}
 
 	/* If no SMT supported, nthreads is forced to 1 */
-- 
2.7.4