@@ -28,6 +28,8 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \
kvm-$(CONFIG_HW_PERF_EVENTS) += pmu-emul.o pmu.o
kvm-$(CONFIG_ARM64_PTR_AUTH) += pauth.o
+kvm-$(CONFIG_TRACING) += hyp_trace.o
+
always-y := hyp_constants.h hyp-constants.s
define rule_gen_hyp_constants
@@ -25,6 +25,7 @@
#define CREATE_TRACE_POINTS
#include "trace_arm.h"
+#include "hyp_trace.h"
#include <linux/uaccess.h>
#include <asm/ptrace.h>
@@ -2330,6 +2331,9 @@ static int __init init_subsystems(void)
kvm_register_perf_callbacks(NULL);
+ err = hyp_trace_init_tracefs();
+ if (err)
+ kvm_err("Failed to initialize Hyp tracing\n");
out:
if (err)
hyp_cpu_pm_exit();
@@ -3,11 +3,15 @@
#include <linux/kbuild.h>
#include <nvhe/memory.h>
#include <nvhe/pkvm.h>
+#include <nvhe/trace.h>
int main(void)
{
DEFINE(STRUCT_HYP_PAGE_SIZE, sizeof(struct hyp_page));
DEFINE(PKVM_HYP_VM_SIZE, sizeof(struct pkvm_hyp_vm));
DEFINE(PKVM_HYP_VCPU_SIZE, sizeof(struct pkvm_hyp_vcpu));
+#ifdef CONFIG_TRACING
+ DEFINE(STRUCT_HYP_BUFFER_PAGE_SIZE, sizeof(struct hyp_buffer_page));
+#endif
return 0;
}
new file mode 100644
@@ -0,0 +1,664 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2024 Google LLC
+ * Author: Vincent Donnefort <vdonnefort@google.com>
+ */
+
+#include <linux/arm-smccc.h>
+#include <linux/percpu-defs.h>
+#include <linux/tracefs.h>
+
+#include <asm/kvm_host.h>
+#include <asm/kvm_hyptrace.h>
+
+#include "hyp_constants.h"
+#include "hyp_trace.h"
+
+#define RB_POLL_MS 100
+
+#define TRACEFS_DIR "hypervisor"
+#define TRACEFS_MODE_WRITE 0640
+#define TRACEFS_MODE_READ 0440
+
+static struct hyp_trace_buffer {
+ struct hyp_trace_desc *desc;
+ struct ring_buffer_writer writer;
+ struct trace_buffer *trace_buffer;
+ size_t desc_size;
+ bool tracing_on;
+ int nr_readers;
+ struct mutex lock;
+} hyp_trace_buffer = {
+ .lock = __MUTEX_INITIALIZER(hyp_trace_buffer.lock),
+};
+
+static size_t hyp_trace_buffer_size = 7 << 10;
+
+/* Number of pages the ring-buffer requires to accommodate for size */
+#define NR_PAGES(size) \
+ ((PAGE_ALIGN(size) >> PAGE_SHIFT) + 1)
+
+static inline bool hyp_trace_buffer_loaded(struct hyp_trace_buffer *hyp_buffer)
+{
+ return !!hyp_buffer->trace_buffer;
+}
+
+static inline bool hyp_trace_buffer_used(struct hyp_trace_buffer *hyp_buffer)
+{
+ return hyp_buffer->nr_readers || hyp_buffer->tracing_on ||
+ !ring_buffer_empty(hyp_buffer->trace_buffer);
+}
+
+static int
+bpage_backing_alloc(struct hyp_buffer_pages_backing *bpage_backing, size_t size)
+{
+ size_t backing_size;
+ void *start;
+
+ backing_size = PAGE_ALIGN(STRUCT_HYP_BUFFER_PAGE_SIZE * NR_PAGES(size) *
+ num_possible_cpus());
+
+ start = alloc_pages_exact(backing_size, GFP_KERNEL_ACCOUNT);
+ if (!start)
+ return -ENOMEM;
+
+ bpage_backing->start = (unsigned long)start;
+ bpage_backing->size = backing_size;
+
+ return 0;
+}
+
+static void
+bpage_backing_free(struct hyp_buffer_pages_backing *bpage_backing)
+{
+ free_pages_exact((void *)bpage_backing->start, bpage_backing->size);
+}
+
+static int __get_reader_page(int cpu)
+{
+ return kvm_call_hyp_nvhe(__pkvm_swap_reader_tracing, cpu);
+}
+
+static void hyp_trace_free_pages(struct hyp_trace_desc *desc)
+{
+ struct rb_page_desc *rb_desc;
+ int cpu, id;
+
+ for_each_rb_page_desc(rb_desc, cpu, &desc->page_desc) {
+ free_page(rb_desc->meta_va);
+ for (id = 0; id < rb_desc->nr_page_va; id++)
+ free_page(rb_desc->page_va[id]);
+ }
+}
+
+static int hyp_trace_alloc_pages(struct hyp_trace_desc *desc, size_t size)
+{
+ int err = 0, cpu, id, nr_pages = NR_PAGES(size);
+ struct trace_page_desc *trace_desc;
+ struct rb_page_desc *rb_desc;
+
+ trace_desc = &desc->page_desc;
+ trace_desc->nr_cpus = 0;
+
+ rb_desc = (struct rb_page_desc *)&trace_desc->__data[0];
+
+ for_each_possible_cpu(cpu) {
+ rb_desc->cpu = cpu;
+ rb_desc->nr_page_va = 0;
+ rb_desc->meta_va = (unsigned long)page_to_virt(alloc_page(GFP_KERNEL));
+ if (!rb_desc->meta_va) {
+ err = -ENOMEM;
+ break;
+ }
+ for (id = 0; id < nr_pages; id++) {
+ rb_desc->page_va[id] = (unsigned long)page_to_virt(alloc_page(GFP_KERNEL));
+ if (!rb_desc->page_va[id]) {
+ err = -ENOMEM;
+ break;
+ }
+ rb_desc->nr_page_va++;
+ }
+ trace_desc->nr_cpus++;
+ rb_desc = __next_rb_page_desc(rb_desc);
+ }
+
+ if (err) {
+ hyp_trace_free_pages(desc);
+ return err;
+ }
+
+ return 0;
+}
+
+static int __load_page(unsigned long va)
+{
+ return kvm_call_hyp_nvhe(__pkvm_host_share_hyp, virt_to_pfn((void *)va), 1);
+}
+
+static void __teardown_page(unsigned long va)
+{
+ WARN_ON(kvm_call_hyp_nvhe(__pkvm_host_unshare_hyp, virt_to_pfn((void *)va), 1));
+}
+
+static void hyp_trace_teardown_pages(struct hyp_trace_desc *desc,
+ int last_cpu)
+{
+ struct rb_page_desc *rb_desc;
+ int cpu, id;
+
+ for_each_rb_page_desc(rb_desc, cpu, &desc->page_desc) {
+ if (cpu > last_cpu)
+ break;
+ __teardown_page(rb_desc->meta_va);
+ for (id = 0; id < rb_desc->nr_page_va; id++)
+ __teardown_page(rb_desc->page_va[id]);
+ }
+}
+
+static int hyp_trace_load_pages(struct hyp_trace_desc *desc)
+{
+ int last_loaded_cpu = 0, cpu, id, err = -EINVAL;
+ struct rb_page_desc *rb_desc;
+
+ for_each_rb_page_desc(rb_desc, cpu, &desc->page_desc) {
+ err = __load_page(rb_desc->meta_va);
+ if (err)
+ break;
+
+ for (id = 0; id < rb_desc->nr_page_va; id++) {
+ err = __load_page(rb_desc->page_va[id]);
+ if (err)
+ break;
+ }
+
+ if (!err)
+ continue;
+
+ for (id--; id >= 0; id--)
+ __teardown_page(rb_desc->page_va[id]);
+
+ last_loaded_cpu = cpu - 1;
+
+ break;
+ }
+
+ if (!err)
+ return 0;
+
+ hyp_trace_teardown_pages(desc, last_loaded_cpu);
+
+ return err;
+}
+
+static int hyp_trace_buffer_load(struct hyp_trace_buffer *hyp_buffer, size_t size)
+{
+ int ret, nr_pages = NR_PAGES(size);
+ struct rb_page_desc *rbdesc;
+ struct hyp_trace_desc *desc;
+ size_t desc_size;
+
+ if (hyp_trace_buffer_loaded(hyp_buffer))
+ return 0;
+
+ desc_size = size_add(offsetof(struct hyp_trace_desc, page_desc),
+ offsetof(struct trace_page_desc, __data));
+ desc_size = size_add(desc_size,
+ size_mul(num_possible_cpus(),
+ struct_size(rbdesc, page_va, nr_pages)));
+ if (desc_size == SIZE_MAX)
+ return -E2BIG;
+
+ /*
+ * The hypervisor will unmap the descriptor from the host to protect the
+ * reading. Page granularity for the allocation ensures no other
+ * useful data will be unmapped.
+ */
+ desc_size = PAGE_ALIGN(desc_size);
+
+ desc = (struct hyp_trace_desc *)alloc_pages_exact(desc_size, GFP_KERNEL);
+ if (!desc)
+ return -ENOMEM;
+
+ ret = hyp_trace_alloc_pages(desc, size);
+ if (ret)
+ goto err_free_desc;
+
+ ret = bpage_backing_alloc(&desc->backing, size);
+ if (ret)
+ goto err_free_pages;
+
+ ret = hyp_trace_load_pages(desc);
+ if (ret)
+ goto err_free_backing;
+
+ ret = kvm_call_hyp_nvhe(__pkvm_load_tracing, (unsigned long)desc, desc_size);
+ if (ret)
+ goto err_teardown_pages;
+
+ hyp_buffer->writer.pdesc = &desc->page_desc;
+ hyp_buffer->writer.get_reader_page = __get_reader_page;
+ hyp_buffer->trace_buffer = ring_buffer_reader(&hyp_buffer->writer);
+ if (!hyp_buffer->trace_buffer) {
+ ret = -ENOMEM;
+ goto err_teardown_tracing;
+ }
+
+ hyp_buffer->desc = desc;
+ hyp_buffer->desc_size = desc_size;
+
+ return 0;
+
+err_teardown_tracing:
+ kvm_call_hyp_nvhe(__pkvm_teardown_tracing);
+err_teardown_pages:
+ hyp_trace_teardown_pages(desc, INT_MAX);
+err_free_backing:
+ bpage_backing_free(&desc->backing);
+err_free_pages:
+ hyp_trace_free_pages(desc);
+err_free_desc:
+ free_pages_exact(desc, desc_size);
+
+ return ret;
+}
+
+static void hyp_trace_buffer_teardown(struct hyp_trace_buffer *hyp_buffer)
+{
+ struct hyp_trace_desc *desc = hyp_buffer->desc;
+ size_t desc_size = hyp_buffer->desc_size;
+
+ if (!hyp_trace_buffer_loaded(hyp_buffer))
+ return;
+
+ if (hyp_trace_buffer_used(hyp_buffer))
+ return;
+
+ if (kvm_call_hyp_nvhe(__pkvm_teardown_tracing))
+ return;
+
+ ring_buffer_free(hyp_buffer->trace_buffer);
+ hyp_trace_teardown_pages(desc, INT_MAX);
+ bpage_backing_free(&desc->backing);
+ hyp_trace_free_pages(desc);
+ free_pages_exact(desc, desc_size);
+ hyp_buffer->trace_buffer = NULL;
+}
+
+static int hyp_trace_start(void)
+{
+ struct hyp_trace_buffer *hyp_buffer = &hyp_trace_buffer;
+ int ret = 0;
+
+ mutex_lock(&hyp_buffer->lock);
+
+ if (hyp_buffer->tracing_on)
+ goto out;
+
+ ret = hyp_trace_buffer_load(hyp_buffer, hyp_trace_buffer_size);
+ if (ret)
+ goto out;
+
+ ret = kvm_call_hyp_nvhe(__pkvm_enable_tracing, true);
+ if (ret) {
+ hyp_trace_buffer_teardown(hyp_buffer);
+ goto out;
+ }
+
+ hyp_buffer->tracing_on = true;
+
+out:
+ mutex_unlock(&hyp_buffer->lock);
+
+ return ret;
+}
+
+static void hyp_trace_stop(void)
+{
+ struct hyp_trace_buffer *hyp_buffer = &hyp_trace_buffer;
+ int ret;
+
+ mutex_lock(&hyp_buffer->lock);
+
+ if (!hyp_buffer->tracing_on)
+ goto end;
+
+ ret = kvm_call_hyp_nvhe(__pkvm_enable_tracing, false);
+ if (!ret) {
+ ring_buffer_poll_writer(hyp_buffer->trace_buffer,
+ RING_BUFFER_ALL_CPUS);
+ hyp_buffer->tracing_on = false;
+ hyp_trace_buffer_teardown(hyp_buffer);
+ }
+
+end:
+ mutex_unlock(&hyp_buffer->lock);
+}
+
+static ssize_t hyp_tracing_on(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ unsigned long val;
+ int ret;
+
+ ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+ if (ret)
+ return ret;
+
+ if (val)
+ ret = hyp_trace_start();
+ else
+ hyp_trace_stop();
+
+ return ret ? ret : cnt;
+}
+
+static ssize_t hyp_tracing_on_read(struct file *filp, char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ char buf[3];
+ int r;
+
+ mutex_lock(&hyp_trace_buffer.lock);
+ r = sprintf(buf, "%d\n", hyp_trace_buffer.tracing_on);
+ mutex_unlock(&hyp_trace_buffer.lock);
+
+ return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
+}
+
+static const struct file_operations hyp_tracing_on_fops = {
+ .write = hyp_tracing_on,
+ .read = hyp_tracing_on_read,
+};
+
+static ssize_t hyp_buffer_size(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ unsigned long val;
+ int ret;
+
+ ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+ if (ret)
+ return ret;
+
+ if (!val)
+ return -EINVAL;
+
+ mutex_lock(&hyp_trace_buffer.lock);
+ hyp_trace_buffer_size = val << 10; /* KB to B */
+ mutex_unlock(&hyp_trace_buffer.lock);
+
+ return cnt;
+}
+
+static ssize_t hyp_buffer_size_read(struct file *filp, char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ char buf[64];
+ int r;
+
+ mutex_lock(&hyp_trace_buffer.lock);
+ r = sprintf(buf, "%lu (%s)\n", hyp_trace_buffer_size >> 10,
+ hyp_trace_buffer_loaded(&hyp_trace_buffer) ?
+ "loaded" : "unloaded");
+ mutex_unlock(&hyp_trace_buffer.lock);
+
+ return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
+}
+
+static const struct file_operations hyp_buffer_size_fops = {
+ .write = hyp_buffer_size,
+ .read = hyp_buffer_size_read,
+};
+
+static void ht_print_trace_time(struct ht_iterator *iter)
+{
+ unsigned long usecs_rem;
+ u64 ts_ns = iter->ts;
+
+ do_div(ts_ns, 1000);
+ usecs_rem = do_div(ts_ns, USEC_PER_SEC);
+
+ trace_seq_printf(&iter->seq, "%5lu.%06lu: ",
+ (unsigned long)ts_ns, usecs_rem);
+}
+
+static void ht_print_trace_cpu(struct ht_iterator *iter)
+{
+ trace_seq_printf(&iter->seq, "[%03d]\t", iter->ent_cpu);
+}
+
+static int ht_print_trace_fmt(struct ht_iterator *iter)
+{
+ if (iter->lost_events)
+ trace_seq_printf(&iter->seq, "CPU:%d [LOST %lu EVENTS]\n",
+ iter->ent_cpu, iter->lost_events);
+
+ ht_print_trace_cpu(iter);
+ ht_print_trace_time(iter);
+
+ return trace_seq_has_overflowed(&iter->seq) ? -EOVERFLOW : 0;
+};
+
+static struct ring_buffer_event *__ht_next_pipe_event(struct ht_iterator *iter)
+{
+ struct ring_buffer_event *evt = NULL;
+ int cpu = iter->cpu;
+
+ if (cpu != RING_BUFFER_ALL_CPUS) {
+ if (ring_buffer_empty_cpu(iter->trace_buffer, cpu))
+ return NULL;
+
+ iter->ent_cpu = cpu;
+
+ return ring_buffer_peek(iter->trace_buffer, cpu, &iter->ts,
+ &iter->lost_events);
+ }
+
+ iter->ts = LLONG_MAX;
+ for_each_possible_cpu(cpu) {
+ struct ring_buffer_event *_evt;
+ unsigned long lost_events;
+ u64 ts;
+
+ if (ring_buffer_empty_cpu(iter->trace_buffer, cpu))
+ continue;
+
+ _evt = ring_buffer_peek(iter->trace_buffer, cpu, &ts,
+ &lost_events);
+ if (!_evt)
+ continue;
+
+ if (ts >= iter->ts)
+ continue;
+
+ iter->ts = ts;
+ iter->ent_cpu = cpu;
+ iter->lost_events = lost_events;
+ evt = _evt;
+ }
+
+ return evt;
+}
+
+static void *ht_next_pipe_event(struct ht_iterator *iter)
+{
+ struct ring_buffer_event *event;
+
+ event = __ht_next_pipe_event(iter);
+ if (!event)
+ return NULL;
+
+ iter->ent = (struct hyp_entry_hdr *)&event->array[1];
+ iter->ent_size = event->array[0];
+
+ return iter;
+}
+
+static ssize_t
+hyp_trace_pipe_read(struct file *file, char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ struct ht_iterator *iter = (struct ht_iterator *)file->private_data;
+ int ret;
+
+copy_to_user:
+ ret = trace_seq_to_user(&iter->seq, ubuf, cnt);
+ if (ret != -EBUSY)
+ return ret;
+
+ trace_seq_init(&iter->seq);
+
+ ret = ring_buffer_wait(iter->trace_buffer, iter->cpu, 0, NULL, NULL);
+ if (ret < 0)
+ return ret;
+
+ while (ht_next_pipe_event(iter)) {
+ int prev_len = iter->seq.seq.len;
+
+ if (ht_print_trace_fmt(iter)) {
+ iter->seq.seq.len = prev_len;
+ break;
+ }
+
+ ring_buffer_consume(iter->trace_buffer, iter->ent_cpu, NULL,
+ NULL);
+ }
+
+ goto copy_to_user;
+}
+
+static void __poll_writer(struct work_struct *work)
+{
+ struct delayed_work *dwork = to_delayed_work(work);
+ struct ht_iterator *iter;
+
+ iter = container_of(dwork, struct ht_iterator, poll_work);
+
+ ring_buffer_poll_writer(iter->trace_buffer, iter->cpu);
+
+ schedule_delayed_work((struct delayed_work *)work,
+ msecs_to_jiffies(RB_POLL_MS));
+}
+
+static int hyp_trace_pipe_open(struct inode *inode, struct file *file)
+{
+ struct hyp_trace_buffer *hyp_buffer = &hyp_trace_buffer;
+ int cpu = (s64)inode->i_private;
+ struct ht_iterator *iter = NULL;
+ int ret;
+
+ mutex_lock(&hyp_buffer->lock);
+
+ if (hyp_buffer->nr_readers == INT_MAX) {
+ ret = -EBUSY;
+ goto unlock;
+ }
+
+ ret = hyp_trace_buffer_load(hyp_buffer, hyp_trace_buffer_size);
+ if (ret)
+ goto unlock;
+
+ iter = kzalloc(sizeof(*iter), GFP_KERNEL);
+ if (!iter) {
+ ret = -ENOMEM;
+ goto unlock;
+ }
+ iter->trace_buffer = hyp_buffer->trace_buffer;
+ iter->cpu = cpu;
+ trace_seq_init(&iter->seq);
+ file->private_data = iter;
+
+ ret = ring_buffer_poll_writer(hyp_buffer->trace_buffer, cpu);
+ if (ret)
+ goto unlock;
+
+ INIT_DELAYED_WORK(&iter->poll_work, __poll_writer);
+ schedule_delayed_work(&iter->poll_work, msecs_to_jiffies(RB_POLL_MS));
+
+ hyp_buffer->nr_readers++;
+
+unlock:
+ if (ret) {
+ hyp_trace_buffer_teardown(hyp_buffer);
+ kfree(iter);
+ }
+
+ mutex_unlock(&hyp_buffer->lock);
+
+ return ret;
+}
+
+static int hyp_trace_pipe_release(struct inode *inode, struct file *file)
+{
+ struct hyp_trace_buffer *hyp_buffer = &hyp_trace_buffer;
+ struct ht_iterator *iter = file->private_data;
+
+ cancel_delayed_work_sync(&iter->poll_work);
+
+ mutex_lock(&hyp_buffer->lock);
+
+ WARN_ON(--hyp_buffer->nr_readers < 0);
+
+ hyp_trace_buffer_teardown(hyp_buffer);
+
+ mutex_unlock(&hyp_buffer->lock);
+
+ kfree(iter);
+
+ return 0;
+}
+
+static const struct file_operations hyp_trace_pipe_fops = {
+ .open = hyp_trace_pipe_open,
+ .read = hyp_trace_pipe_read,
+ .release = hyp_trace_pipe_release,
+ .llseek = no_llseek,
+};
+
+int hyp_trace_init_tracefs(void)
+{
+ struct dentry *root, *per_cpu_root;
+ char per_cpu_name[16];
+ long cpu;
+
+ if (!is_protected_kvm_enabled())
+ return 0;
+
+ root = tracefs_create_dir(TRACEFS_DIR, NULL);
+ if (!root) {
+ pr_err("Failed to create tracefs "TRACEFS_DIR"/\n");
+ return -ENODEV;
+ }
+
+ tracefs_create_file("tracing_on", TRACEFS_MODE_WRITE, root, NULL,
+ &hyp_tracing_on_fops);
+
+ tracefs_create_file("buffer_size_kb", TRACEFS_MODE_WRITE, root, NULL,
+ &hyp_buffer_size_fops);
+
+ tracefs_create_file("trace_pipe", TRACEFS_MODE_WRITE, root,
+ (void *)RING_BUFFER_ALL_CPUS, &hyp_trace_pipe_fops);
+
+ per_cpu_root = tracefs_create_dir("per_cpu", root);
+ if (!per_cpu_root) {
+ pr_err("Failed to create tracefs folder "TRACEFS_DIR"/per_cpu/\n");
+ return -ENODEV;
+ }
+
+ for_each_possible_cpu(cpu) {
+ struct dentry *per_cpu_dir;
+
+ snprintf(per_cpu_name, sizeof(per_cpu_name), "cpu%ld", cpu);
+ per_cpu_dir = tracefs_create_dir(per_cpu_name, per_cpu_root);
+ if (!per_cpu_dir) {
+ pr_warn("Failed to create tracefs "TRACEFS_DIR"/per_cpu/cpu%ld\n",
+ cpu);
+ continue;
+ }
+
+ tracefs_create_file("trace_pipe", TRACEFS_MODE_READ, per_cpu_dir,
+ (void *)cpu, &hyp_trace_pipe_fops);
+ }
+
+ return 0;
+}
new file mode 100644
@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ARM64_KVM_HYP_TRACE_H__
+#define __ARM64_KVM_HYP_TRACE_H__
+
+#include <linux/trace_seq.h>
+#include <linux/workqueue.h>
+
+struct ht_iterator {
+ struct trace_buffer *trace_buffer;
+ int cpu;
+ struct hyp_entry_hdr *ent;
+ unsigned long lost_events;
+ int ent_cpu;
+ size_t ent_size;
+ u64 ts;
+ void *spare;
+ size_t copy_leftover;
+ struct trace_seq seq;
+ struct delayed_work poll_work;
+};
+
+#ifdef CONFIG_TRACING
+int hyp_trace_init_tracefs(void);
+#else
+static inline int hyp_trace_init_tracefs(void) { return 0; }
+#endif
+#endif
When running with KVM protected mode, the hypervisor is able to generate events into tracefs compatible ring-buffers. Plug those ring-buffers to tracefs. The interface is found in hyp/ and contains the same hierarchy as any host instances easing the support by existing user-space tools. This currently doesn't provide any event support which will come later. Signed-off-by: Vincent Donnefort <vdonnefort@google.com>