[PATCH v4 17/19] KVM: selftests: Print vCPU affinity on timeout during IRQ test

[Josh Hilke <jrhilke@google.com>]

Add kvm_print_vcpu_affinity() to lib/kvm_util.c to print the physical
CPU affinity of a vCPU thread in a human-readable format.

Use this new helper in tools/testing/selftests/kvm/irq_test.c to print
the vCPU's affinity if it times out waiting for an interrupt while vCPU
migration (-m) is enabled.  This provides valuable context for debugging
IRQ delivery timeouts when vCPUs are being actively migrated across
physical CPUs.

Signed-off-by: Josh Hilke <jrhilke@google.com>
---
 .../testing/selftests/kvm/include/kvm_util.h  |  1 +
 tools/testing/selftests/kvm/irq_test.c        |  2 +
 tools/testing/selftests/kvm/lib/kvm_util.c    | 49 +++++++++++++++++++
 3 files changed, 52 insertions(+)

diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index f725ab0ed4f9..0ec82088bc43 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -1119,6 +1119,7 @@ static inline int pin_self_to_any_cpu(void)
 void kvm_print_vcpu_pinning_help(void);
 void kvm_parse_vcpu_pinning(const char *pcpus_string, uint32_t vcpu_to_pcpu[],
 			    int nr_vcpus);
+void kvm_print_vcpu_affinity(struct kvm_vcpu *vcpu, pid_t tid);
 
 unsigned long vm_compute_max_gfn(struct kvm_vm *vm);
 unsigned int vm_calc_num_guest_pages(enum vm_guest_mode mode, size_t size);
diff --git a/tools/testing/selftests/kvm/irq_test.c b/tools/testing/selftests/kvm/irq_test.c
index f653317022e3..0db4ea4eb1ef 100644
--- a/tools/testing/selftests/kvm/irq_test.c
+++ b/tools/testing/selftests/kvm/irq_test.c
@@ -309,6 +309,8 @@ int main(int argc, char **argv)
 				printf("  is interrupt NMI: %s\n", do_use_nmi ? "true" : "false");
 				if (irq_affinity)
 					printf("  irq_cpu: %d\n", irq_cpu);
+				if (migrate_vcpus)
+					kvm_print_vcpu_affinity(vcpu, vcpu_tids[vcpu->id]);
 
 				TEST_FAIL("vCPU %d timed out waiting for IRQ from GSI %d (Vector 0x%x) !\n",
 					  vcpu->id, gsi, vector);
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 29cd649a54d5..b2e534f331e2 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -15,6 +15,7 @@
 #include <sys/resource.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/sysinfo.h>
 #include <unistd.h>
 #include <linux/kernel.h>
 
@@ -662,6 +663,54 @@ void kvm_print_vcpu_pinning_help(void)
 	       "     (default: no pinning)\n", name, name);
 }
 
+void kvm_print_vcpu_affinity(struct kvm_vcpu *vcpu, pid_t tid)
+{
+	int nprocs = get_nprocs();
+	bool first_range = true;
+	int i, start = -1;
+	cpu_set_t cpus;
+
+	kvm_sched_getaffinity(tid, sizeof(cpus), &cpus);
+
+	/*
+	 * Output format examples:
+	 * - Single CPU:  "vCPU 0 (TID 1234) affined to pCPU(s): 2"
+	 * - List:        "vCPU 0 (TID 1234) affined to pCPU(s): 0,2,4"
+	 * - Range:       "vCPU 0 (TID 1234) affined to pCPU(s): 0-7"
+	 * - Mixed:       "vCPU 0 (TID 1234) affined to pCPU(s): 0-3,8,10-12"
+	 */
+	printf("vCPU %u (TID %d) affined to pCPU(s): ", vcpu->id, tid);
+
+	for (i = 0; i <= nprocs; i++) {
+		/*
+		 * Iterate to nprocs (inclusive) to ensure that if the last pCPU
+		 * is part of a range, the 'else' block triggers one final time
+		 * to flush that range to stdout.
+		 */
+		if (i < nprocs && CPU_ISSET(i, &cpus)) {
+			if (start == -1)
+				start = i;
+			continue;
+		}
+
+		if (start != -1) {
+			int end = i - 1;
+
+			if (!first_range)
+				printf(",");
+
+			if (start == end)
+				printf("%d", start);
+			else
+				printf("%d-%d", start, end);
+
+			start = -1;
+			first_range = false;
+		}
+	}
+	printf("\n");
+}
+
 void pin_task_to_random_cpu(pthread_t task, cpu_set_t *possible_cpus)
 {
 	int target_idx;
-- 
2.54.0.929.g9b7fa37559-goog