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AJvYcCWUX91eT0uNEE4O9YpAY2wVpxiLUydcFMuqJyJWuZMkSA4iy5QOJqyDNWB59gYWO6mXWY4i0yaiyM+1tU4=@vger.kernel.org X-Gm-Message-State: AOJu0YwSC/yyVLZBRJs6NNLCZ7EnSzMNuZn/d+IwJRteNGXAtfXGQhjX tZ7cOoUgTYErTgFLBOgnZCqX/Yh+RKG751uh+FN9kxfDIhOybXmrrgRR0Yy4kJ4UyZcP3xbq+Zk IwoD7hYfiLdxNl1cqFmTBuA== X-Google-Smtp-Source: AGHT+IGtoiMOJbbUGluKcrrf2jpd/NA0bAXHTN5z3JSiX93+rkt/dUPjaiqGSvXO5tGCjwTSEh0V65pmrBuPuVG1 X-Received: from wmht22.prod.google.com ([2002:a05:600c:41d6:b0:46e:3190:9ce]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:a11:b0:46e:33a6:46b2 with SMTP id 5b1f17b1804b1-46e71109edfmr23711595e9.12.1759498741833; Fri, 03 Oct 2025 06:39:01 -0700 (PDT) Date: Fri, 3 Oct 2025 14:38:02 +0100 In-Reply-To: <20251003133825.2068970-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251003133825.2068970-1-vdonnefort@google.com> X-Mailer: git-send-email 2.51.0.618.g983fd99d29-goog Message-ID: <20251003133825.2068970-6-vdonnefort@google.com> Subject: [PATCH v7 05/28] tracing: Introduce trace remotes From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-trace-kernel@vger.kernel.org, maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, jstultz@google.com, qperret@google.com, will@kernel.org, aneesh.kumar@kernel.org, kernel-team@android.com, linux-kernel@vger.kernel.org, Vincent Donnefort Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h new file mode 100644 index 000000000000..feb3433c2128 --- /dev/null +++ b/include/linux/trace_remote.h @@ -0,0 +1,80 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef _LINUX_TRACE_REMOTE_H +#define _LINUX_TRACE_REMOTE_H + +#include + +/** + * struct trace_remote_callbacks - Callbacks used by Tracefs to control th= e remote + * + * @load_trace_buffer: Called before Tracefs accesses the trace buffer fo= r the first + * time. Must return a &trace_buffer_desc + * (most likely filled with trace_remote_alloc_buffer()) + * @unload_trace_buffer: + * Called once Tracefs has no use for the trace buffer + * (most likely call trace_remote_free_buffer()) + * @enable_tracing: Called on Tracefs tracing_on. It is expected from the + * remote to allow writing. + * @swap_reader_page: Called when Tracefs consumes a new page from a + * ring-buffer. It is expected from the remote to isolate a + * new reader-page from the @cpu ring-buffer. + */ +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); +}; + +/** + * trace_remote_register() - Register a Tracefs remote + * + * A trace remote is an entity, outside of the kernel (most likely firmwar= e or + * hypervisor) capable of writing events into a Tracefs compatible ring-bu= ffer. + * The kernel would then act as a reader. + * + * The registered remote will be found under the Tracefs directory + * remotes/. + * + * @name: Name of the remote, used for the Tracefs remotes/ directory. + * @cbs: Set of callbacks used to control the remote. + * @priv: Private data, passed to each callback from @cbs. + * @events: Array of events. &remote_event.name and &remote_event.id must = be + * filled by the caller. + * @nr_events: Number of events in the @events array. + * + * Return: 0 on success, negative error code on failure. + */ +int trace_remote_register(const char *name, struct trace_remote_callbacks = *cbs, void *priv); + +/** + * trace_remote_alloc_buffer() - Dynamically allocate a trace buffer + * + * Helper to dynamically allocate a set of pages (enough to cover @buffer_= size) + * for each CPU from @cpumask and fill @desc. Most likely called from + * &trace_remote_callbacks.load_trace_buffer. + * + * @desc: Uninitialized trace_buffer_desc + * @desc_size: Size of the trace_buffer_desc. Must be at least equal to + * trace_buffer_desc_size() + * @buffer_size: Size in bytes of each per-CPU ring-buffer + * @cpumask: CPUs to allocate a ring-buffer for + * + * Return: 0 on success, negative error code on failure. + */ +int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t desc_= size, size_t buffer_size, + const struct cpumask *cpumask); + +/** + * trace_remote_free_buffer() - Free trace buffer allocated with + * trace_remote_alloc_buffer() + * + * Most likely called from &trace_remote_callbacks.unload_trace_buffer. + * + * @desc: Descriptor of the per-CPU ring-buffers, originally filled by + * trace_remote_alloc_buffer() + */ +void trace_remote_free_buffer(struct trace_buffer_desc *desc); + +#endif diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index d2c79da81e4f..99af56d39eaf 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -1238,4 +1238,7 @@ config HIST_TRIGGERS_DEBUG =20 source "kernel/trace/rv/Kconfig" =20 +config TRACE_REMOTE + bool + endif # FTRACE diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index dcb4e02afc5f..6dab341acc46 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -110,4 +110,5 @@ obj-$(CONFIG_FPROBE_EVENTS) +=3D trace_fprobe.o obj-$(CONFIG_TRACEPOINT_BENCHMARK) +=3D trace_benchmark.o obj-$(CONFIG_RV) +=3D rv/ =20 +obj-$(CONFIG_TRACE_REMOTE) +=3D trace_remote.o libftrace-y :=3D ftrace.o diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index b3c94fbaf002..ec0cdbe96766 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8949,7 +8949,7 @@ static struct dentry *tracing_dentry_percpu(struct tr= ace_array *tr, int cpu) return tr->percpu_dir; } =20 -static struct dentry * +struct dentry * trace_create_cpu_file(const char *name, umode_t mode, struct dentry *paren= t, void *data, long cpu, const struct file_operations *fops) { diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 5f4bed5842f9..a3386cf0c760 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -672,6 +672,12 @@ 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); =20 =20 /** diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c new file mode 100644 index 000000000000..3d76a4d7d5f5 --- /dev/null +++ b/kernel/trace/trace_remote.c @@ -0,0 +1,568 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2025 - Google LLC + * Author: Vincent Donnefort + */ + +#include +#include +#include +#include +#include +#include +#include + +#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 =3D &remote->rb_remote; + + lockdep_assert_held(&remote->lock); + + if (trace_remote_loaded(remote)) + return 0; + + remote->trace_buffer_desc =3D remote->cbs->load_trace_buffer(remote->trac= e_buffer_size, + remote->priv); + if (IS_ERR(remote->trace_buffer_desc)) + return PTR_ERR(remote->trace_buffer_desc); + + rb_remote->desc =3D remote->trace_buffer_desc; + rb_remote->swap_reader_page =3D remote->cbs->swap_reader_page; + rb_remote->priv =3D remote->priv; + remote->trace_buffer =3D ring_buffer_alloc_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 =3D 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 =3D trace_remote_load(remote); + if (ret) + return ret; + + ret =3D remote->cbs->enable_tracing(true, remote->priv); + if (ret) { + trace_remote_try_unload(remote); + return ret; + } + + remote->tracing_on =3D 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 =3D 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 =3D false; + trace_remote_try_unload(remote); + + return 0; +} + +static ssize_t +tracing_on_write(struct file *filp, const char __user *ubuf, size_t cnt, l= off_t *ppos) +{ + struct trace_remote *remote =3D filp->private_data; + unsigned long val; + int ret; + + ret =3D kstrtoul_from_user(ubuf, cnt, 10, &val); + if (ret) + return ret; + + guard(mutex)(&remote->lock); + + ret =3D 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 =3D 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 =3D filp->private_data; + unsigned long val; + int ret; + + ret =3D 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 =3D val; + + return cnt; +} + +static int buffer_size_kb_show(struct seq_file *s, void *unused) +{ + struct trace_remote *remote =3D 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 int trace_remote_get(struct trace_remote *remote, int cpu) +{ + int ret; + + if (remote->nr_readers =3D=3D UINT_MAX) + return -EBUSY; + + ret =3D trace_remote_load(remote); + if (ret) + return ret; + + remote->nr_readers++; + + return 0; +} + +static void trace_remote_put(struct trace_remote *remote) +{ + if (WARN_ON(!remote->nr_readers)) + return; + + remote->nr_readers--; + if (remote->nr_readers) + return; + + trace_remote_try_unload(remote); +} + +static void __poll_remote(struct work_struct *work) +{ + struct delayed_work *dwork =3D to_delayed_work(work); + struct trace_remote_iterator *iter; + + iter =3D 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, enum tri_type typ= e) +{ + struct trace_remote_iterator *iter =3D NULL; + int ret; + + lockdep_assert_held(&remote->lock); + + + ret =3D trace_remote_get(remote, cpu); + if (ret) + return ERR_PTR(ret); + + /* Test the CPU */ + ret =3D ring_buffer_poll_remote(remote->trace_buffer, cpu); + if (ret) + goto err; + + iter =3D kzalloc(sizeof(*iter), GFP_KERNEL); + if (iter) { + iter->remote =3D remote; + iter->cpu =3D 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 =3D -ENOMEM; + +err: + kfree(iter); + trace_remote_put(remote); + + return ERR_PTR(ret); +} + +static void trace_remote_iter_free(struct trace_remote_iterator *iter) +{ + struct trace_remote *remote; + + if (!iter) + return; + + remote =3D iter->remote; + + lockdep_assert_held(&remote->lock); + + kfree(iter); + trace_remote_put(remote); +} + +static bool trace_remote_iter_read_event(struct trace_remote_iterator *ite= r) +{ + struct trace_buffer *trace_buffer =3D iter->remote->trace_buffer; + int cpu =3D iter->cpu; + + if (cpu !=3D 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 =3D cpu; + return true; + } + + iter->ts =3D 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 >=3D iter->ts) + continue; + + iter->ts =3D ts; + iter->evt_cpu =3D cpu; + iter->lost_events =3D lost_events; + } + + return iter->ts !=3D U64_MAX; +} + +static int trace_remote_iter_print(struct trace_remote_iterator *iter) +{ + unsigned long usecs_rem; + u64 ts =3D 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 =3D 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 =3D inode->i_private; + struct trace_remote_iterator *iter; + int cpu =3D RING_BUFFER_ALL_CPUS; + + if (inode->i_cdev) + cpu =3D (long)inode->i_cdev - 1; + + guard(mutex)(&remote->lock); + iter =3D trace_remote_iter(remote, cpu); + filp->private_data =3D 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 =3D filp->private_data; + struct trace_remote *remote =3D iter->remote; + + guard(mutex)(&remote->lock); + + trace_remote_iter_free(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 =3D filp->private_data; + struct trace_buffer *trace_buffer =3D iter->remote->trace_buffer; + int ret; + +copy_to_user: + ret =3D trace_seq_to_user(&iter->seq, ubuf, cnt); + if (ret !=3D -EBUSY) + return ret; + + trace_seq_init(&iter->seq); + + ret =3D ring_buffer_wait(trace_buffer, iter->cpu, 0, NULL, NULL); + if (ret < 0) + return ret; + + while (trace_remote_iter_next(iter)) { + while (trace_remote_iter_read_event(iter)) { + int prev_len =3D iter->seq.seq.len; + + if (trace_remote_iter_print_event(iter)) { + iter->seq.seq.len =3D 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 =3D { + .open =3D trace_pipe_open, + .read =3D trace_pipe_read, + .release =3D 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 =3D false; + int cpu; + + guard(mutex)(&lock); + + if (!root) { + root =3D tracefs_create_dir(TRACEFS_DIR, NULL); + if (!root) { + pr_err("Failed to create tracefs dir "TRACEFS_DIR"\n"); + return -ENOMEM; + } + root_inited =3D true; + } + + remote_d =3D 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, re= mote, + &buffer_size_kb_fops) || + !trace_create_file("trace_pipe", TRACEFS_MODE_READ, remote_d, remote, + &trace_pipe_fops)) + goto err; + + percpu_d =3D 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 =3D 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, remot= e, cpu, + &trace_pipe_fops)) + goto err; + } + + return 0; + +err: + if (root_inited) { + tracefs_remove(root); + root =3D 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 =3D kzalloc(sizeof(*remote), GFP_KERNEL); + if (!remote) + return -ENOMEM; + + remote->cbs =3D cbs; + remote->priv =3D priv; + remote->trace_buffer_size =3D 7 << 10; + remote->poll_ms =3D 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 =3D 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 desc_= size, size_t buffer_size, + const struct cpumask *cpumask) +{ + unsigned int nr_pages =3D max(DIV_ROUND_UP(buffer_size, PAGE_SIZE), 2UL) = + 1; + void *desc_end =3D desc + desc_size; + struct ring_buffer_desc *rb_desc; + int cpu, ret =3D -ENOMEM; + + if (desc_size < struct_size(desc, __data, 0)) + return -EINVAL; + + desc->nr_cpus =3D 0; + desc->struct_len =3D struct_size(desc, __data, 0); + + rb_desc =3D (struct ring_buffer_desc *)&desc->__data[0]; + + for_each_cpu(cpu, cpumask) { + unsigned int id; + + if ((void *)rb_desc + struct_size(rb_desc, page_va, nr_pages) > desc_end= ) { + ret =3D -EINVAL; + goto err; + } + + rb_desc->cpu =3D cpu; + rb_desc->nr_page_va =3D 0; + rb_desc->meta_va =3D (unsigned long)__get_free_page(GFP_KERNEL); + if (!rb_desc->meta_va) + goto err; + + for (id =3D 0; id < nr_pages; id++) { + rb_desc->page_va[id] =3D (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 +=3D offsetof(struct ring_buffer_desc, page_va); + desc->struct_len +=3D struct_size(rb_desc, page_va, rb_desc->nr_page_va); + rb_desc =3D __next_ring_buffer_desc(rb_desc); + } + + return 0; + +err: + trace_remote_free_buffer(desc); + return ret; +} --=20 2.51.0.618.g983fd99d29-goog