A trace remote relies on ring-buffer remotes to read and control compatible tracing buffers, written by entity such as firmware or hypervisor.
Add a Tracefs directory remotes/ that contains all instances of trace remotes. Each instance follows the same hierarchy as any other to ease the support by existing user-space tools. This currently does not provide any event support, which will come later. Signed-off-by: Vincent Donnefort <vdonnef...@google.com> diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h new file mode 100644 index 000000000000..de043a6f2fe0 --- /dev/null +++ b/include/linux/trace_remote.h @@ -0,0 +1,21 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef _LINUX_TRACE_REMOTE_H +#define _LINUX_TRACE_REMOTE_H + +#include <linux/ring_buffer.h> + +struct trace_remote_callbacks { + struct trace_buffer_desc * + (*load_trace_buffer)(unsigned long size, void *priv); + void (*unload_trace_buffer)(struct trace_buffer_desc *desc, void *priv); + int (*enable_tracing)(bool enable, void *priv); + int (*swap_reader_page)(unsigned int cpu, void *priv); +}; + +int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs, void *priv); +int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t size, + const struct cpumask *cpumask); +void trace_remote_free_buffer(struct trace_buffer_desc *desc); + +#endif diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index a3f35c7d83b6..2fcc86c7fe7e 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -1215,4 +1215,7 @@ config HIST_TRIGGERS_DEBUG source "kernel/trace/rv/Kconfig" +config TRACE_REMOTE + bool + endif # FTRACE diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index 057cd975d014..b8204ae93744 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -110,4 +110,5 @@ obj-$(CONFIG_FPROBE_EVENTS) += trace_fprobe.o obj-$(CONFIG_TRACEPOINT_BENCHMARK) += trace_benchmark.o obj-$(CONFIG_RV) += rv/ +obj-$(CONFIG_TRACE_REMOTE) += trace_remote.o libftrace-y := ftrace.o diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 5b8db27fb6ef..52c89462a73c 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8842,7 +8842,7 @@ static struct dentry *tracing_dentry_percpu(struct trace_array *tr, int cpu) return tr->percpu_dir; } -static struct dentry * +struct dentry * trace_create_cpu_file(const char *name, umode_t mode, struct dentry *parent, void *data, long cpu, const struct file_operations *fops) { diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 79be1995db44..f357e7e1ae71 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -670,6 +670,12 @@ struct dentry *trace_create_file(const char *name, struct dentry *parent, void *data, const struct file_operations *fops); +struct dentry *trace_create_cpu_file(const char *name, + umode_t mode, + struct dentry *parent, + void *data, + long cpu, + const struct file_operations *fops); int tracing_init_dentry(void); diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c new file mode 100644 index 000000000000..1a4786b7970c --- /dev/null +++ b/kernel/trace/trace_remote.c @@ -0,0 +1,518 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2025 - Google LLC + * Author: Vincent Donnefort <vdonnef...@google.com> + */ + +#include <linux/kstrtox.h> +#include <linux/lockdep.h> +#include <linux/mutex.h> +#include <linux/tracefs.h> +#include <linux/trace_remote.h> +#include <linux/trace_seq.h> +#include <linux/types.h> + +#include "trace.h" + +#define TRACEFS_DIR "remotes" +#define TRACEFS_MODE_WRITE 0640 +#define TRACEFS_MODE_READ 0440 + +struct trace_remote_iterator { + struct trace_remote *remote; + struct trace_seq seq; + struct delayed_work poll_work; + unsigned long lost_events; + u64 ts; + int cpu; + int evt_cpu; +}; + +struct trace_remote { + struct trace_remote_callbacks *cbs; + void *priv; + struct trace_buffer *trace_buffer; + struct trace_buffer_desc *trace_buffer_desc; + unsigned long trace_buffer_size; + struct ring_buffer_remote rb_remote; + struct mutex lock; + unsigned int nr_readers; + unsigned int poll_ms; + bool tracing_on; +}; + +static bool trace_remote_loaded(struct trace_remote *remote) +{ + return remote->trace_buffer; +} + +static int trace_remote_load(struct trace_remote *remote) +{ + struct ring_buffer_remote *rb_remote = &remote->rb_remote; + + lockdep_assert_held(&remote->lock); + + if (trace_remote_loaded(remote)) + return 0; + + remote->trace_buffer_desc = remote->cbs->load_trace_buffer(remote->trace_buffer_size, + remote->priv); + if (IS_ERR(remote->trace_buffer_desc)) + return PTR_ERR(remote->trace_buffer_desc); + + rb_remote->desc = remote->trace_buffer_desc; + rb_remote->swap_reader_page = remote->cbs->swap_reader_page; + rb_remote->priv = remote->priv; + remote->trace_buffer = ring_buffer_remote(rb_remote); + if (!remote->trace_buffer) { + remote->cbs->unload_trace_buffer(remote->trace_buffer_desc, remote->priv); + return -ENOMEM; + } + + return 0; +} + +static void trace_remote_try_unload(struct trace_remote *remote) +{ + lockdep_assert_held(&remote->lock); + + if (!trace_remote_loaded(remote)) + return; + + /* The buffer is being read or writable */ + if (remote->nr_readers || remote->tracing_on) + return; + + /* The buffer has readable data */ + if (!ring_buffer_empty(remote->trace_buffer)) + return; + + ring_buffer_free(remote->trace_buffer); + remote->trace_buffer = NULL; + remote->cbs->unload_trace_buffer(remote->trace_buffer_desc, remote->priv); +} + +static int trace_remote_enable_tracing(struct trace_remote *remote) +{ + int ret; + + lockdep_assert_held(&remote->lock); + + if (remote->tracing_on) + return 0; + + ret = trace_remote_load(remote); + if (ret) + return ret; + + ret = remote->cbs->enable_tracing(true, remote->priv); + if (ret) { + trace_remote_try_unload(remote); + return ret; + } + + remote->tracing_on = true; + + return 0; +} + +static int trace_remote_disable_tracing(struct trace_remote *remote) +{ + int ret; + + lockdep_assert_held(&remote->lock); + + if (!remote->tracing_on) + return 0; + + ret = remote->cbs->enable_tracing(false, remote->priv); + if (ret) + return ret; + + ring_buffer_poll_remote(remote->trace_buffer, RING_BUFFER_ALL_CPUS); + remote->tracing_on = false; + trace_remote_try_unload(remote); + + return 0; +} + +static ssize_t +tracing_on_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos) +{ + struct trace_remote *remote = filp->private_data; + unsigned long val; + int ret; + + ret = kstrtoul_from_user(ubuf, cnt, 10, &val); + if (ret) + return ret; + + guard(mutex)(&remote->lock); + + ret = val ? trace_remote_enable_tracing(remote) : trace_remote_disable_tracing(remote); + if (ret) + return ret; + + return cnt; +} +static int tracing_on_show(struct seq_file *s, void *unused) +{ + struct trace_remote *remote = s->private; + + seq_printf(s, "%d\n", remote->tracing_on); + + return 0; +} +DEFINE_SHOW_STORE_ATTRIBUTE(tracing_on); + +static ssize_t buffer_size_kb_write(struct file *filp, const char __user *ubuf, size_t cnt, + loff_t *ppos) +{ + struct trace_remote *remote = filp->private_data; + unsigned long val; + int ret; + + ret = kstrtoul_from_user(ubuf, cnt, 10, &val); + if (ret) + return ret; + + /* KiB to Bytes */ + if (!val || check_shl_overflow(val, 10, &val)) + return -EINVAL; + + guard(mutex)(&remote->lock); + + remote->trace_buffer_size = val; + + return cnt; +} + +static int buffer_size_kb_show(struct seq_file *s, void *unused) +{ + struct trace_remote *remote = s->private; + + seq_printf(s, "%lu (%s)\n", remote->trace_buffer_size >> 10, + trace_remote_loaded(remote) ? "loaded" : "unloaded"); + + return 0; +} +DEFINE_SHOW_STORE_ATTRIBUTE(buffer_size_kb); + +static void __poll_remote(struct work_struct *work) +{ + struct delayed_work *dwork = to_delayed_work(work); + struct trace_remote_iterator *iter; + + iter = container_of(dwork, struct trace_remote_iterator, poll_work); + ring_buffer_poll_remote(iter->remote->trace_buffer, iter->cpu); + schedule_delayed_work((struct delayed_work *)work, + msecs_to_jiffies(iter->remote->poll_ms)); +} + +static struct trace_remote_iterator *trace_remote_iter(struct trace_remote *remote, int cpu) +{ + struct trace_remote_iterator *iter; + int ret; + + if (remote->nr_readers == ULONG_MAX) + return ERR_PTR(-EBUSY); + + ret = trace_remote_load(remote); + if (ret) + return ERR_PTR(ret); + + /* Test the CPU */ + ret = ring_buffer_poll_remote(remote->trace_buffer, cpu); + if (ret) + goto err; + + iter = kzalloc(sizeof(*iter), GFP_KERNEL); + if (iter) { + remote->nr_readers++; + + iter->remote = remote; + iter->cpu = cpu; + trace_seq_init(&iter->seq); + INIT_DELAYED_WORK(&iter->poll_work, __poll_remote); + schedule_delayed_work(&iter->poll_work, msecs_to_jiffies(remote->poll_ms)); + + return iter; + } + ret = -ENOMEM; + +err: + trace_remote_try_unload(remote); + + return ERR_PTR(ret); +} + +static bool trace_remote_iter_next(struct trace_remote_iterator *iter) +{ + struct trace_buffer *trace_buffer = iter->remote->trace_buffer; + int cpu = iter->cpu; + + if (cpu != RING_BUFFER_ALL_CPUS) { + if (ring_buffer_empty_cpu(trace_buffer, cpu)) + return false; + + if (!ring_buffer_peek(trace_buffer, cpu, &iter->ts, &iter->lost_events)) + return false; + + iter->evt_cpu = cpu; + return true; + } + + iter->ts = U64_MAX; + for_each_possible_cpu(cpu) { + unsigned long lost_events; + u64 ts; + + if (ring_buffer_empty_cpu(trace_buffer, cpu)) + continue; + + if (!ring_buffer_peek(trace_buffer, cpu, &ts, &lost_events)) + continue; + + if (ts >= iter->ts) + continue; + + iter->ts = ts; + iter->evt_cpu = cpu; + iter->lost_events = lost_events; + } + + return iter->ts != U64_MAX; +} + +static int trace_remote_iter_print(struct trace_remote_iterator *iter) +{ + unsigned long usecs_rem; + u64 ts = iter->ts; + + if (iter->lost_events) + trace_seq_printf(&iter->seq, "CPU:%d [LOST %lu EVENTS]\n", + iter->evt_cpu, iter->lost_events); + + do_div(ts, 1000); + usecs_rem = do_div(ts, USEC_PER_SEC); + + trace_seq_printf(&iter->seq, "[%03d]\t%5llu.%06lu: ", iter->evt_cpu, + ts, usecs_rem); + + return trace_seq_has_overflowed(&iter->seq) ? -EOVERFLOW : 0; +} + +static int trace_pipe_open(struct inode *inode, struct file *filp) +{ + struct trace_remote *remote = inode->i_private; + struct trace_remote_iterator *iter; + int cpu = RING_BUFFER_ALL_CPUS; + + if (inode->i_cdev) + cpu = (long)inode->i_cdev - 1; + + guard(mutex)(&remote->lock); + iter = trace_remote_iter(remote, cpu); + filp->private_data = iter; + + return IS_ERR(iter) ? PTR_ERR(iter) : 0; +} + +static int trace_pipe_release(struct inode *inode, struct file *filp) +{ + struct trace_remote_iterator *iter = filp->private_data; + struct trace_remote *remote = iter->remote; + + guard(mutex)(&remote->lock); + + cancel_delayed_work_sync(&iter->poll_work); + remote->nr_readers--; + trace_remote_try_unload(remote); + kfree(iter); + + return 0; +} + +static ssize_t trace_pipe_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos) +{ + struct trace_remote_iterator *iter = filp->private_data; + struct trace_buffer *trace_buffer = iter->remote->trace_buffer; + 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(trace_buffer, iter->cpu, 0, NULL, NULL); + if (ret < 0) + return ret; + + while (trace_remote_iter_next(iter)) { + int prev_len = iter->seq.seq.len; + + if (trace_remote_iter_print(iter)) { + iter->seq.seq.len = prev_len; + break; + } + + ring_buffer_consume(trace_buffer, iter->evt_cpu, NULL, NULL); + } + + goto copy_to_user; +} + +static const struct file_operations trace_pipe_fops = { + .open = trace_pipe_open, + .read = trace_pipe_read, + .release = trace_pipe_release, +}; + +static int trace_remote_init_tracefs(const char *name, struct trace_remote *remote) +{ + struct dentry *remote_d, *percpu_d; + static struct dentry *root; + static DEFINE_MUTEX(lock); + bool root_inited = false; + int cpu; + + guard(mutex)(&lock); + + if (!root) { + root = tracefs_create_dir(TRACEFS_DIR, NULL); + if (!root) { + pr_err("Failed to create tracefs dir "TRACEFS_DIR"\n"); + goto err; + } + root_inited = true; + } + + remote_d = tracefs_create_dir(name, root); + if (!remote_d) { + pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/\n", name); + goto err; + } + + if (!trace_create_file("tracing_on", TRACEFS_MODE_WRITE, remote_d, remote, + &tracing_on_fops) || + !trace_create_file("buffer_size_kb", TRACEFS_MODE_WRITE, remote_d, remote, + &buffer_size_kb_fops) || + !trace_create_file("trace_pipe", TRACEFS_MODE_READ, remote_d, remote, + &trace_pipe_fops)) + goto err; + + percpu_d = tracefs_create_dir("per_cpu", remote_d); + if (!percpu_d) { + pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/per_cpu/\n", name); + goto err; + } + + for_each_possible_cpu(cpu) { + struct dentry *cpu_d; + char cpu_name[16]; + + snprintf(cpu_name, sizeof(cpu_name), "cpu%d", cpu); + cpu_d = tracefs_create_dir(cpu_name, percpu_d); + if (!cpu_d) { + pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/percpu/cpu%d\n", + name, cpu); + goto err; + } + + if (!trace_create_cpu_file("trace_pipe", TRACEFS_MODE_READ, cpu_d, remote, cpu, + &trace_pipe_fops)) + goto err; + } + + return 0; + +err: + if (root_inited) { + tracefs_remove(root); + root = NULL; + } else { + tracefs_remove(remote_d); + } + + return -ENOMEM; +} + +int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs, void *priv) +{ + struct trace_remote *remote; + + remote = kzalloc(sizeof(*remote), GFP_KERNEL); + if (!remote) + return -ENOMEM; + + remote->cbs = cbs; + remote->priv = priv; + remote->trace_buffer_size = 7 << 10; + remote->poll_ms = 100; + mutex_init(&remote->lock); + + if (trace_remote_init_tracefs(name, remote)) { + kfree(remote); + return -ENOMEM; + } + + return 0; +} + +void trace_remote_free_buffer(struct trace_buffer_desc *desc) +{ + struct ring_buffer_desc *rb_desc; + int cpu; + + for_each_ring_buffer_desc(rb_desc, cpu, desc) { + unsigned int id; + + free_page(rb_desc->meta_va); + + for (id = 0; id < rb_desc->nr_page_va; id++) + free_page(rb_desc->page_va[id]); + } +} + +int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t size, + const struct cpumask *cpumask) +{ + int nr_pages = (PAGE_ALIGN(size) / PAGE_SIZE) + 1; + struct ring_buffer_desc *rb_desc; + int cpu; + + desc->nr_cpus = 0; + desc->struct_len = offsetof(struct trace_buffer_desc, __data); + + rb_desc = (struct ring_buffer_desc *)&desc->__data[0]; + + for_each_cpu(cpu, cpumask) { + unsigned int id; + + rb_desc->cpu = cpu; + rb_desc->nr_page_va = 0; + rb_desc->meta_va = (unsigned long)__get_free_page(GFP_KERNEL); + if (!rb_desc->meta_va) + goto err; + + for (id = 0; id < nr_pages; id++) { + rb_desc->page_va[id] = (unsigned long)__get_free_page(GFP_KERNEL); + if (!rb_desc->page_va[id]) + goto err; + + rb_desc->nr_page_va++; + } + desc->nr_cpus++; + desc->struct_len += offsetof(struct ring_buffer_desc, page_va); + desc->struct_len += sizeof(rb_desc->page_va[0]) * rb_desc->nr_page_va; + rb_desc = __next_ring_buffer_desc(rb_desc); + } + + return 0; + +err: + trace_remote_free_buffer(desc); + return -ENOMEM; +} -- 2.49.0.1101.gccaa498523-goog