kvm powerpc/book3s-apiv2: Introduce kvm-hv specific PMU

Introduce a new PMU named 'kvm-hv' inside a new module named 'kvm-hv-pmu'
to report Book3s kvm-hv specific performance counters. This will expose
KVM-HV specific performance attributes to user-space via kernel's PMU
infrastructure and would enableusers to monitor active kvm-hv based guests.

The patch creates necessary scaffolding to for the new PMU callbacks and
introduces the new kernel module name 'kvm-hv-pmu' which is built with
CONFIG_KVM_BOOK3S_HV_PMU. The patch doesn't introduce any perf-events yet,
which will be introduced in later patches

Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250416162740.93143-5-vaibhav@linux.ibm.com

arch/powerpc/kvm/Kconfig

@@ -83,6 +83,7 @@ config KVM_BOOK3S_64_HV
 	depends on KVM_BOOK3S_64 && PPC_POWERNV
 	select KVM_BOOK3S_HV_POSSIBLE
 	select KVM_GENERIC_MMU_NOTIFIER
+	select KVM_BOOK3S_HV_PMU
 	select CMA
 	help
 	  Support running unmodified book3s_64 guest kernels in
@@ -171,6 +172,18 @@ config KVM_BOOK3S_HV_NESTED_PMU_WORKAROUND
 	  those buggy L1s which saves the L2 state, at the cost of performance
 	  in all nested-capable guest entry/exit.
 
+config KVM_BOOK3S_HV_PMU
+	tristate "Hypervisor Perf events for KVM Book3s-HV"
+	depends on KVM_BOOK3S_64_HV
+	help
+	  Enable Book3s-HV Hypervisor Perf events PMU named 'kvm-hv'. These
+	  Perf events give an overview of hypervisor performance overall
+	  instead of a specific guests. Currently the PMU reports
+	  L0-Hypervisor stats on a kvm-hv enabled PSeries LPAR like:
+	  * Total/Used Guest-Heap
+	  * Total/Used Guest Page-table Memory
+	  * Total amount of Guest Page-table Memory reclaimed
+
 config KVM_BOOKE_HV
 	bool
 

arch/powerpc/perf/Makefile

@@ -18,6 +18,8 @@ obj-$(CONFIG_HV_PERF_CTRS) += hv-24x7.o hv-gpci.o hv-common.o
 
 obj-$(CONFIG_VPA_PMU) += vpa-pmu.o
 
+obj-$(CONFIG_KVM_BOOK3S_HV_PMU) += kvm-hv-pmu.o
+
 obj-$(CONFIG_PPC_8xx) += 8xx-pmu.o
 
 obj-$(CONFIG_PPC64)		+= $(obj64-y)

arch/powerpc/perf/kvm-hv-pmu.c

@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Description: PMUs specific to running nested KVM-HV guests
+ * on Book3S processors (specifically POWER9 and later).
+ */
+
+#define pr_fmt(fmt)  "kvmppc-pmu: " fmt
+
+#include "asm-generic/local64.h"
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/ratelimit.h>
+#include <linux/kvm_host.h>
+#include <linux/gfp_types.h>
+#include <linux/pgtable.h>
+#include <linux/perf_event.h>
+#include <linux/spinlock_types.h>
+#include <linux/spinlock.h>
+
+#include <asm/types.h>
+#include <asm/kvm_ppc.h>
+#include <asm/kvm_book3s.h>
+#include <asm/mmu.h>
+#include <asm/pgalloc.h>
+#include <asm/pte-walk.h>
+#include <asm/reg.h>
+#include <asm/plpar_wrappers.h>
+#include <asm/firmware.h>
+
+enum kvmppc_pmu_eventid {
+	KVMPPC_EVENT_MAX,
+};
+
+static struct attribute *kvmppc_pmu_events_attr[] = {
+	NULL,
+};
+
+static const struct attribute_group kvmppc_pmu_events_group = {
+	.name = "events",
+	.attrs = kvmppc_pmu_events_attr,
+};
+
+PMU_FORMAT_ATTR(event, "config:0");
+static struct attribute *kvmppc_pmu_format_attr[] = {
+	&format_attr_event.attr,
+	NULL,
+};
+
+static struct attribute_group kvmppc_pmu_format_group = {
+	.name = "format",
+	.attrs = kvmppc_pmu_format_attr,
+};
+
+static const struct attribute_group *kvmppc_pmu_attr_groups[] = {
+	&kvmppc_pmu_events_group,
+	&kvmppc_pmu_format_group,
+	NULL,
+};
+
+static int kvmppc_pmu_event_init(struct perf_event *event)
+{
+	unsigned int config = event->attr.config;
+
+	pr_debug("%s: Event(%p) id=%llu cpu=%x on_cpu=%x config=%u",
+		 __func__, event, event->id, event->cpu,
+		 event->oncpu, config);
+
+	if (event->attr.type != event->pmu->type)
+		return -ENOENT;
+
+	if (config >= KVMPPC_EVENT_MAX)
+		return -EINVAL;
+
+	local64_set(&event->hw.prev_count, 0);
+	local64_set(&event->count, 0);
+
+	return 0;
+}
+
+static void kvmppc_pmu_del(struct perf_event *event, int flags)
+{
+}
+
+static int kvmppc_pmu_add(struct perf_event *event, int flags)
+{
+	return 0;
+}
+
+static void kvmppc_pmu_read(struct perf_event *event)
+{
+}
+
+/* L1 wide counters PMU */
+static struct pmu kvmppc_pmu = {
+	.module = THIS_MODULE,
+	.task_ctx_nr = perf_sw_context,
+	.name = "kvm-hv",
+	.event_init = kvmppc_pmu_event_init,
+	.add = kvmppc_pmu_add,
+	.del = kvmppc_pmu_del,
+	.read = kvmppc_pmu_read,
+	.attr_groups = kvmppc_pmu_attr_groups,
+	.type = -1,
+};
+
+static int __init kvmppc_register_pmu(void)
+{
+	int rc = -EOPNOTSUPP;
+
+	/* only support events for nestedv2 right now */
+	if (kvmhv_is_nestedv2()) {
+		/* Register the pmu */
+		rc = perf_pmu_register(&kvmppc_pmu, kvmppc_pmu.name, -1);
+		if (rc)
+			goto out;
+
+		pr_info("Registered kvm-hv pmu");
+	}
+
+out:
+	return rc;
+}
+
+static void __exit kvmppc_unregister_pmu(void)
+{
+	if (kvmhv_is_nestedv2()) {
+		if (kvmppc_pmu.type != -1)
+			perf_pmu_unregister(&kvmppc_pmu);
+
+		pr_info("kvmhv_pmu unregistered.\n");
+	}
+}
+
+module_init(kvmppc_register_pmu);
+module_exit(kvmppc_unregister_pmu);
+MODULE_DESCRIPTION("KVM PPC Book3s-hv PMU");
+MODULE_AUTHOR("Vaibhav Jain <vaibhav@linux.ibm.com>");
+MODULE_LICENSE("GPL");