arm64: Add support for KVM_ARM_VCPU_PMU_V3_SET_PMU

The KVM_ARM_VCPU_PMU_V3_CTRL(KVM_ARM_VCPU_PMU_V3_SET_PMU) VCPU ioctl is
used to assign a physical PMU to the events that KVM creates when emulating
the PMU for that VCPU. This is useful on heterogeneous systems, when there
is more than one hardware PMU present. All VCPUs must have the same PMU
assigned.

The assumption that is made in the implementation is that the user will pin
the kvmtool process on a set of CPUs that share the same PMU. This allows
kvmtool to set the same PMU for all VCPUs from the main thread, instead of
in the individual VCPU threads. If a VCPU thread migrates to a CPU which
has a different a PMU than the CPU on which the main thread was executing
when the PMU was set, the KVM_RUN ioctl will fail with kvm_run.exit_reason
set to KVM_EXIT_FAIL_ENTRY, and kvm_run.fail_entry will be populated with
the physical CPU ID on which the VCPU tried to execute.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Link: https://lore.kernel.org/r/20220412133231.35355-11-alexandru.elisei@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

2 files changed, 148 insertions, 3 deletions

diff --git a/arm/aarch64/include/kvm/kvm-config-arch.h b/arm/aarch64/include/kvm/kvm-config-arch.h
index 3d39cd6d..b08ee60e 100644
--- a/arm/aarch64/include/kvm/kvm-config-arch.h
+++ b/arm/aarch64/include/kvm/kvm-config-arch.h
@@ -5,7 +5,9 @@
 	OPT_BOOLEAN('\0', "aarch32", &(cfg)->aarch32_guest,		\
 			"Run AArch32 guest"),				\
 	OPT_BOOLEAN('\0', "pmu", &(cfg)->has_pmuv3,			\
-			"Create PMUv3 device"),				\
+			"Create PMUv3 device. The emulated PMU will be" \
+			" set to the PMU associated with the"		\
+			" main thread"),				\
 	OPT_BOOLEAN('\0', "disable-mte", &(cfg)->mte_disabled,		\
 			"Disable Memory Tagging Extension"),		\
 	OPT_U64('\0', "kaslr-seed", &(cfg)->kaslr_seed,			\
diff --git a/arm/aarch64/pmu.c b/arm/aarch64/pmu.c
index ac5b7bcd..869a150c 100644
--- a/arm/aarch64/pmu.c
+++ b/arm/aarch64/pmu.c
@@ -1,3 +1,9 @@
+#include <dirent.h>
+#include <sched.h>
+
+#include "linux/cpumask.h"
+#include "linux/err.h"
+
 #include "kvm/fdt.h"
 #include "kvm/kvm.h"
 #include "kvm/kvm-cpu.h"
@@ -7,6 +13,17 @@
 
 #include "asm/pmu.h"
 
+static bool pmu_has_attr(struct kvm_cpu *vcpu, u64 attr)
+{
+	struct kvm_device_attr pmu_attr = {
+		.group	= KVM_ARM_VCPU_PMU_V3_CTRL,
+		.attr	= attr,
+	};
+	int ret = ioctl(vcpu->vcpu_fd, KVM_HAS_DEVICE_ATTR, &pmu_attr);
+
+	return ret == 0;
+}
+
 static void set_pmu_attr(struct kvm_cpu *vcpu, void *addr, u64 attr)
 {
 	struct kvm_device_attr pmu_attr = {
@@ -16,8 +33,7 @@ static void set_pmu_attr(struct kvm_cpu *vcpu, void *addr, u64 attr)
 	};
 	int ret;
 
-	ret = ioctl(vcpu->vcpu_fd, KVM_HAS_DEVICE_ATTR, &pmu_attr);
-	if (!ret) {
+	if (pmu_has_attr(vcpu, attr)) {
 		ret = ioctl(vcpu->vcpu_fd, KVM_SET_DEVICE_ATTR, &pmu_attr);
 		if (ret)
 			die_perror("PMU KVM_SET_DEVICE_ATTR");
@@ -26,11 +42,124 @@ static void set_pmu_attr(struct kvm_cpu *vcpu, void *addr, u64 attr)
 	}
 }
 
+#define SYS_EVENT_SOURCE	"/sys/bus/event_source/devices/"
+/*
+ * int is 32 bits and INT_MAX translates in decimal to 2 * 10^9.
+ * Make room for newline and NUL.
+ */
+#define PMU_ID_MAXLEN		12
+
+/*
+ * In the case of homogeneous systems, there only one hardware PMU, and all
+ * VCPUs will use the same PMU, regardless of where the attribute gets set.
+ *
+ * For heterogeneous systems, the assumption is that the user has pinned the VM
+ * (via taskset or similar) to a set of CPUs that share the same hardware PMU.
+ * This simplifies things for kvmtool, as correctness is not affected by setting
+ * the PMU for each VCPU from the main thread, instead of setting it from each
+ * individual VCPU thread.
+ */
+static int find_pmu(void)
+{
+	char buf[PMU_ID_MAXLEN];
+	struct dirent *dirent;
+	char *cpulist, *path;
+	int pmu_id = -ENXIO;
+	unsigned long val;
+	cpumask_t cpumask;
+	ssize_t fd_sz;
+	int this_cpu;
+	int fd, ret;
+	DIR *dir;
+
+	memset(buf, 0, PMU_ID_MAXLEN);
+
+	this_cpu = sched_getcpu();
+	if (this_cpu < 0)
+		return -errno;
+
+	cpulist = calloc(1, PAGE_SIZE);
+	if (!cpulist)
+		die_perror("calloc");
+
+	path = calloc(1, PAGE_SIZE);
+	if (!path)
+		die_perror("calloc");
+
+	dir = opendir(SYS_EVENT_SOURCE);
+	if (!dir) {
+		pmu_id = -errno;
+		goto out_free;
+	}
+
+	/* Make the compiler happy by copying the NUL terminating byte. */
+	strncpy(path, SYS_EVENT_SOURCE, strlen(SYS_EVENT_SOURCE) + 1);
+
+	while ((dirent = readdir(dir))) {
+		if (dirent->d_type != DT_LNK)
+			continue;
+
+		strcat(path, dirent->d_name);
+		strcat(path, "/cpus");
+		fd = open(path, O_RDONLY);
+		if (fd < 0)
+			goto next_dir;
+
+		fd_sz = read_file(fd, cpulist, PAGE_SIZE);
+		if (fd_sz < 0) {
+			pmu_id = -errno;
+			goto out_free;
+		}
+		close(fd);
+
+		ret = cpulist_parse(cpulist, &cpumask);
+		if (ret) {
+			pmu_id = ret;
+			goto out_free;
+		}
+
+		if (!cpumask_test_cpu(this_cpu, &cpumask))
+			goto next_dir;
+
+		strcpy(&path[strlen(path) - 4], "type");
+		fd = open(path, O_RDONLY);
+		if (fd < 0)
+			goto next_dir;
+
+		fd_sz = read_file(fd, buf, PMU_ID_MAXLEN - 1);
+		if (fd_sz < 0) {
+			pmu_id = -errno;
+			goto out_free;
+		}
+		close(fd);
+
+		val = strtoul(buf, NULL, 10);
+		if (val > INT_MAX) {
+			pmu_id = -EOVERFLOW;
+			goto out_free;
+		}
+		pmu_id = (int)val;
+		pr_debug("Using PMU %s (id %d)", dirent->d_name, pmu_id);
+		break;
+
+next_dir:
+		/* Reset path. */
+		memset(&path[strlen(SYS_EVENT_SOURCE)], '\0',
+		       strlen(path) - strlen(SYS_EVENT_SOURCE));
+	}
+
+out_free:
+	free(path);
+	free(cpulist);
+	return pmu_id;
+}
+
 void pmu__generate_fdt_nodes(void *fdt, struct kvm *kvm)
 {
 	const char compatible[] = "arm,armv8-pmuv3";
 	int irq = KVM_ARM_PMUv3_PPI;
 	struct kvm_cpu *vcpu;
+	int pmu_id = -ENXIO;
 	int i;
 
 	u32 cpu_mask = (((1 << kvm->nrcpus) - 1) << GIC_FDT_IRQ_PPI_CPU_SHIFT) \
@@ -44,9 +173,23 @@ void pmu__generate_fdt_nodes(void *fdt, struct kvm *kvm)
 	if (!kvm->cfg.arch.has_pmuv3)
 		return;
 
+	if (pmu_has_attr(kvm->cpus[0], KVM_ARM_VCPU_PMU_V3_SET_PMU)) {
+		pmu_id = find_pmu();
+		if (pmu_id < 0) {
+			pr_debug("Failed to find a PMU (errno: %d), "
+				 "PMU events might not work", -pmu_id);
+		}
+	}
+
 	for (i = 0; i < kvm->nrcpus; i++) {
 		vcpu = kvm->cpus[i];
 		set_pmu_attr(vcpu, &irq, KVM_ARM_VCPU_PMU_V3_IRQ);
+		/*
+		 * PMU IDs 0-5 are reserved; a positive value means a PMU was
+		 * found.
+		 */
+		if (pmu_id > 0)
+			set_pmu_attr(vcpu, &pmu_id, KVM_ARM_VCPU_PMU_V3_SET_PMU);
 		set_pmu_attr(vcpu, NULL, KVM_ARM_VCPU_PMU_V3_INIT);
 	}