tile: support delivering NMIs for multicore backtrace

A new hypervisor service was added some time ago (MDE 4.2.1 or
later, or MDE 4.3 or later) that allows cores to request NMIs
to be delivered to other cores.  Use this facility to deliver
a request that causes a backtrace to be generated on each core,
and hook it into the magic SysRq functionality.

Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>

5 files changed, 125 insertions, 1 deletions

diff --git a/arch/tile/kernel/hvglue.S b/arch/tile/kernel/hvglue.S
index 2ab456622391..d78ee2ad610c 100644
--- a/arch/tile/kernel/hvglue.S
+++ b/arch/tile/kernel/hvglue.S
@@ -71,4 +71,5 @@ gensym hv_flush_all, 0x6e0, 32
 gensym hv_get_ipi_pte, 0x700, 32
 gensym hv_set_pte_super_shift, 0x720, 32
 gensym hv_console_set_ipi, 0x7e0, 32
-gensym hv_glue_internals, 0x800, 30720
+gensym hv_send_nmi, 0x820, 32
+gensym hv_glue_internals, 0x820, 30688
diff --git a/arch/tile/kernel/hvglue_trace.c b/arch/tile/kernel/hvglue_trace.c
index 85c74ad29312..add0d71395c6 100644
--- a/arch/tile/kernel/hvglue_trace.c
+++ b/arch/tile/kernel/hvglue_trace.c
@@ -75,6 +75,7 @@
 #define hv_get_ipi_pte _hv_get_ipi_pte
 #define hv_set_pte_super_shift _hv_set_pte_super_shift
 #define hv_console_set_ipi _hv_console_set_ipi
+#define hv_send_nmi _hv_send_nmi
 #include <hv/hypervisor.h>
 #undef hv_init
 #undef hv_install_context
@@ -134,6 +135,7 @@
 #undef hv_get_ipi_pte
 #undef hv_set_pte_super_shift
 #undef hv_console_set_ipi
+#undef hv_send_nmi
 
 /*
  * Provide macros based on <linux/syscalls.h> to provide a wrapper
@@ -264,3 +266,5 @@ HV_WRAP9(int, hv_flush_remote, HV_PhysAddr, cache_pa,
 	 HV_VirtAddr, tlb_va, unsigned long, tlb_length,
 	 unsigned long, tlb_pgsize, unsigned long*, tlb_cpumask,
 	 HV_Remote_ASID*, asids, int, asidcount)
+HV_WRAP3(HV_NMI_Info, hv_send_nmi, HV_Coord, tile, unsigned long, info,
+	 __hv64, flags)
diff --git a/arch/tile/kernel/intvec_64.S b/arch/tile/kernel/intvec_64.S
index 5b67efcecabd..800b91d3f9dc 100644
--- a/arch/tile/kernel/intvec_64.S
+++ b/arch/tile/kernel/intvec_64.S
@@ -515,6 +515,10 @@ intvec_\vecname:
 	.ifc \c_routine, handle_perf_interrupt
 	mfspr   r2, AUX_PERF_COUNT_STS
 	.endif
+	.ifc \c_routine, do_nmi
+	mfspr   r2, SPR_SYSTEM_SAVE_K_2   /* nmi type */
+	.else
+	.endif
 	.endif
 	.endif
 	.endif
@@ -1571,3 +1575,5 @@ intrpt_start:
 
 	/* Synthetic interrupt delivered only by the simulator */
 	int_hand     INT_BREAKPOINT, BREAKPOINT, do_breakpoint
+	/* Synthetic interrupt delivered by hv */
+	int_hand     INT_NMI_DWNCL, NMI_DWNCL, do_nmi, handle_nmi
diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c
index b403c2e3e263..0dddcf7e5bfa 100644
--- a/arch/tile/kernel/process.c
+++ b/arch/tile/kernel/process.c
@@ -27,6 +27,7 @@
 #include <linux/kernel.h>
 #include <linux/tracehook.h>
 #include <linux/signal.h>
+#include <linux/delay.h>
 #include <linux/context_tracking.h>
 #include <asm/stack.h>
 #include <asm/switch_to.h>
@@ -574,3 +575,103 @@ void show_regs(struct pt_regs *regs)
 
 	dump_stack_regs(regs);
 }
+
+/* To ensure stack dump on tiles occurs one by one. */
+static DEFINE_SPINLOCK(backtrace_lock);
+/* To ensure no backtrace occurs before all of the stack dump are done. */
+static atomic_t backtrace_cpus;
+/* The cpu mask to avoid reentrance. */
+static struct cpumask backtrace_mask;
+
+void do_nmi_dump_stack(struct pt_regs *regs)
+{
+	int is_idle = is_idle_task(current) && !in_interrupt();
+	int cpu;
+
+	nmi_enter();
+	cpu = smp_processor_id();
+	if (WARN_ON_ONCE(!cpumask_test_and_clear_cpu(cpu, &backtrace_mask)))
+		goto done;
+
+	spin_lock(&backtrace_lock);
+	if (is_idle)
+		pr_info("CPU: %d idle\n", cpu);
+	else
+		show_regs(regs);
+	spin_unlock(&backtrace_lock);
+	atomic_dec(&backtrace_cpus);
+done:
+	nmi_exit();
+}
+
+#ifdef __tilegx__
+void arch_trigger_all_cpu_backtrace(bool self)
+{
+	struct cpumask mask;
+	HV_Coord tile;
+	unsigned int timeout;
+	int cpu;
+	int ongoing;
+	HV_NMI_Info info[NR_CPUS];
+
+	ongoing = atomic_cmpxchg(&backtrace_cpus, 0, num_online_cpus() - 1);
+	if (ongoing != 0) {
+		pr_err("Trying to do all-cpu backtrace.\n");
+		pr_err("But another all-cpu backtrace is ongoing (%d cpus left)\n",
+		       ongoing);
+		if (self) {
+			pr_err("Reporting the stack on this cpu only.\n");
+			dump_stack();
+		}
+		return;
+	}
+
+	cpumask_copy(&mask, cpu_online_mask);
+	cpumask_clear_cpu(smp_processor_id(), &mask);
+	cpumask_copy(&backtrace_mask, &mask);
+
+	/* Backtrace for myself first. */
+	if (self)
+		dump_stack();
+
+	/* Tentatively dump stack on remote tiles via NMI. */
+	timeout = 100;
+	while (!cpumask_empty(&mask) && timeout) {
+		for_each_cpu(cpu, &mask) {
+			tile.x = cpu_x(cpu);
+			tile.y = cpu_y(cpu);
+			info[cpu] = hv_send_nmi(tile, TILE_NMI_DUMP_STACK, 0);
+			if (info[cpu].result == HV_NMI_RESULT_OK)
+				cpumask_clear_cpu(cpu, &mask);
+		}
+
+		mdelay(10);
+		timeout--;
+	}
+
+	/* Warn about cpus stuck in ICS and decrement their counts here. */
+	if (!cpumask_empty(&mask)) {
+		for_each_cpu(cpu, &mask) {
+			switch (info[cpu].result) {
+			case HV_NMI_RESULT_FAIL_ICS:
+				pr_warn("Skipping stack dump of cpu %d in ICS at pc %#llx\n",
+					cpu, info[cpu].pc);
+				break;
+			case HV_NMI_RESULT_FAIL_HV:
+				pr_warn("Skipping stack dump of cpu %d in hypervisor\n",
+					cpu);
+				break;
+			case HV_ENOSYS:
+				pr_warn("Hypervisor too old to allow remote stack dumps.\n");
+				goto skip_for_each;
+			default:  /* should not happen */
+				pr_warn("Skipping stack dump of cpu %d [%d,%#llx]\n",
+					cpu, info[cpu].result, info[cpu].pc);
+				break;
+			}
+		}
+skip_for_each:
+		atomic_sub(cpumask_weight(&mask), &backtrace_cpus);
+	}
+}
+#endif /* __tilegx_ */
diff --git a/arch/tile/kernel/traps.c b/arch/tile/kernel/traps.c
index 312fc134c1cb..855f7316f1ee 100644
--- a/arch/tile/kernel/traps.c
+++ b/arch/tile/kernel/traps.c
@@ -395,6 +395,18 @@ done:
 	exception_exit(prev_state);
 }
 
+void do_nmi(struct pt_regs *regs, int fault_num, unsigned long reason)
+{
+	switch (reason) {
+	case TILE_NMI_DUMP_STACK:
+		do_nmi_dump_stack(regs);
+		break;
+	default:
+		panic("Unexpected do_nmi type %ld", reason);
+		return;
+	}
+}
+
 void kernel_double_fault(int dummy, ulong pc, ulong lr, ulong sp, ulong r52)
 {
 	_dump_stack(dummy, pc, lr, sp, r52);