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AJvYcCV0/i8rMi/rMHzgJps+J9Oud0B+Zts5WOi+yzfY3gqC1DwK2pr8OFh6Jet1NCDhGhJh/J3tdCpn9t3KOizqLIi0JTg= X-Gm-Message-State: AOJu0YyoPiWDrts8xasqmRMQ8RZiY44+YZEApjRscge85V/DFJrRPFX9 68Z1t5X77Hsacgc0ui0Xp9gEFxNlEFd0IpKN1XC84YQz8o1Xgc+xFVVXIHA0Pq9MnpIAoMw6SXW Fg71VotOntmUhbqWw6g== X-Google-Smtp-Source: AGHT+IH4aAdFCbQpVTxOIxmJnKvlunl2HlLx9B7Ji/MUNPmgnfqGAPV7aMMW3i4CtjntM1+7sFIFi2tQe3Uv+aKw X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:adf:e187:0:b0:343:9761:2ad5 with SMTP id az7-20020adfe187000000b0034397612ad5mr10353wrb.11.1712425033134; Sat, 06 Apr 2024 10:37:13 -0700 (PDT) Date: Sat, 6 Apr 2024 18:36:46 +0100 In-Reply-To: <20240406173649.3210836-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20240406173649.3210836-1-vdonnefort@google.com> X-Mailer: git-send-email 2.44.0.478.gd926399ef9-goog Message-ID: <20240406173649.3210836-3-vdonnefort@google.com> Subject: [PATCH v20 2/5] ring-buffer: Introducing ring-buffer mapping functions From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: mathieu.desnoyers@efficios.com, kernel-team@android.com, rdunlap@infradead.org, Vincent Donnefort , linux-mm@kvack.org X-Stat-Signature: n3tp8ojxxnq9wsgw98p1pp994kgpyiwy X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: F3B9A4000E X-Rspam-User: X-HE-Tag: 1712425034-243826 X-HE-Meta: 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 6tiMaxjO 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: In preparation for allowing the user-space to map a ring-buffer, add a set of mapping functions: ring_buffer_{map,unmap}() And controls on the ring-buffer: ring_buffer_map_get_reader() /* swap reader and head */ Mapping the ring-buffer also involves: A unique ID for each subbuf of the ring-buffer, currently they are only identified through their in-kernel VA. A meta-page, where are stored ring-buffer statistics and a description for the current reader The linear mapping exposes the meta-page, and each subbuf of the ring-buffer, ordered following their unique ID, assigned during the first mapping. Once mapped, no subbuf can get in or out of the ring-buffer: the buffer size will remain unmodified and the splice enabling functions will in reality simply memcpy the data instead of swapping subbufs. CC: Signed-off-by: Vincent Donnefort diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index dc5ae4e96aee..96d2140b471e 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -6,6 +6,8 @@ #include #include +#include + struct trace_buffer; struct ring_buffer_iter; @@ -223,4 +225,8 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node); #define trace_rb_cpu_prepare NULL #endif +int ring_buffer_map(struct trace_buffer *buffer, int cpu, + struct vm_area_struct *vma); +int ring_buffer_unmap(struct trace_buffer *buffer, int cpu); +int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu); #endif /* _LINUX_RING_BUFFER_H */ diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h new file mode 100644 index 000000000000..ffcd8dfcaa4f --- /dev/null +++ b/include/uapi/linux/trace_mmap.h @@ -0,0 +1,46 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _TRACE_MMAP_H_ +#define _TRACE_MMAP_H_ + +#include + +/** + * struct trace_buffer_meta - Ring-buffer Meta-page description + * @meta_page_size: Size of this meta-page. + * @meta_struct_len: Size of this structure. + * @subbuf_size: Size of each sub-buffer. + * @nr_subbufs: Number of subbfs in the ring-buffer, including the reader. + * @reader.lost_events: Number of events lost at the time of the reader swap. + * @reader.id: subbuf ID of the current reader. ID range [0 : @nr_subbufs - 1] + * @reader.read: Number of bytes read on the reader subbuf. + * @flags: Placeholder for now, 0 until new features are supported. + * @entries: Number of entries in the ring-buffer. + * @overrun: Number of entries lost in the ring-buffer. + * @read: Number of entries that have been read. + * @Reserved1: Reserved for future use. + * @Reserved2: Reserved for future use. + */ +struct trace_buffer_meta { + __u32 meta_page_size; + __u32 meta_struct_len; + + __u32 subbuf_size; + __u32 nr_subbufs; + + struct { + __u64 lost_events; + __u32 id; + __u32 read; + } reader; + + __u64 flags; + + __u64 entries; + __u64 overrun; + __u64 read; + + __u64 Reserved1; + __u64 Reserved2; +}; + +#endif /* _TRACE_MMAP_H_ */ diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index cc9ebe593571..793ecc454039 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include #include @@ -26,6 +27,7 @@ #include #include #include +#include #include #include @@ -338,6 +340,7 @@ struct buffer_page { local_t entries; /* entries on this page */ unsigned long real_end; /* real end of data */ unsigned order; /* order of the page */ + u32 id; /* ID for external mapping */ struct buffer_data_page *page; /* Actual data page */ }; @@ -484,6 +487,12 @@ struct ring_buffer_per_cpu { u64 read_stamp; /* pages removed since last reset */ unsigned long pages_removed; + + unsigned int mapped; + struct mutex mapping_lock; + unsigned long *subbuf_ids; /* ID to subbuf VA */ + struct trace_buffer_meta *meta_page; + /* ring buffer pages to update, > 0 to add, < 0 to remove */ long nr_pages_to_update; struct list_head new_pages; /* new pages to add */ @@ -1599,6 +1608,7 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu) init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters); init_waitqueue_head(&cpu_buffer->irq_work.waiters); init_waitqueue_head(&cpu_buffer->irq_work.full_waiters); + mutex_init(&cpu_buffer->mapping_lock); bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), GFP_KERNEL, cpu_to_node(cpu)); @@ -1789,8 +1799,6 @@ bool ring_buffer_time_stamp_abs(struct trace_buffer *buffer) return buffer->time_stamp_abs; } -static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer); - static inline unsigned long rb_page_entries(struct buffer_page *bpage) { return local_read(&bpage->entries) & RB_WRITE_MASK; @@ -5211,6 +5219,22 @@ static void rb_clear_buffer_page(struct buffer_page *page) page->read = 0; } +static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + struct trace_buffer_meta *meta = cpu_buffer->meta_page; + + meta->reader.read = cpu_buffer->reader_page->read; + meta->reader.id = cpu_buffer->reader_page->id; + meta->reader.lost_events = cpu_buffer->lost_events; + + meta->entries = local_read(&cpu_buffer->entries); + meta->overrun = local_read(&cpu_buffer->overrun); + meta->read = cpu_buffer->read; + + /* Some archs do not have data cache coherency between kernel and user-space */ + flush_dcache_folio(virt_to_folio(cpu_buffer->meta_page)); +} + static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) { @@ -5255,6 +5279,9 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) cpu_buffer->lost_events = 0; cpu_buffer->last_overrun = 0; + if (cpu_buffer->mapped) + rb_update_meta_page(cpu_buffer); + rb_head_page_activate(cpu_buffer); cpu_buffer->pages_removed = 0; } @@ -5469,6 +5496,12 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a, cpu_buffer_a = buffer_a->buffers[cpu]; cpu_buffer_b = buffer_b->buffers[cpu]; + /* It's up to the callers to not try to swap mapped buffers */ + if (WARN_ON_ONCE(cpu_buffer_a->mapped || cpu_buffer_b->mapped)) { + ret = -EBUSY; + goto out; + } + /* At least make sure the two buffers are somewhat the same */ if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages) goto out; @@ -5733,7 +5766,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer, * Otherwise, we can simply swap the page with the one passed in. */ if (read || (len < (commit - read)) || - cpu_buffer->reader_page == cpu_buffer->commit_page) { + cpu_buffer->reader_page == cpu_buffer->commit_page || + cpu_buffer->mapped) { struct buffer_data_page *rpage = cpu_buffer->reader_page->page; unsigned int rpos = read; unsigned int pos = 0; @@ -5956,6 +5990,11 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) cpu_buffer = buffer->buffers[cpu]; + if (cpu_buffer->mapped) { + err = -EBUSY; + goto error; + } + /* Update the number of pages to match the new size */ nr_pages = old_size * buffer->buffers[cpu]->nr_pages; nr_pages = DIV_ROUND_UP(nr_pages, buffer->subbuf_size); @@ -6057,6 +6096,358 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) } EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set); +static int rb_alloc_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + struct page *page; + + if (cpu_buffer->meta_page) + return 0; + + page = alloc_page(GFP_USER | __GFP_ZERO); + if (!page) + return -ENOMEM; + + cpu_buffer->meta_page = page_to_virt(page); + + return 0; +} + +static void rb_free_meta_page(struct ring_buffer_per_cpu *cpu_buffer) +{ + unsigned long addr = (unsigned long)cpu_buffer->meta_page; + + free_page(addr); + cpu_buffer->meta_page = NULL; +} + +static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer, + unsigned long *subbuf_ids) +{ + struct trace_buffer_meta *meta = cpu_buffer->meta_page; + unsigned int nr_subbufs = cpu_buffer->nr_pages + 1; + struct buffer_page *first_subbuf, *subbuf; + int id = 0; + + subbuf_ids[id] = (unsigned long)cpu_buffer->reader_page->page; + cpu_buffer->reader_page->id = id++; + + first_subbuf = subbuf = rb_set_head_page(cpu_buffer); + do { + if (WARN_ON(id >= nr_subbufs)) + break; + + subbuf_ids[id] = (unsigned long)subbuf->page; + subbuf->id = id; + + rb_inc_page(&subbuf); + id++; + } while (subbuf != first_subbuf); + + /* install subbuf ID to kern VA translation */ + cpu_buffer->subbuf_ids = subbuf_ids; + + /* __rb_map_vma() pads the meta-page to align it with the sub-buffers */ + meta->meta_page_size = PAGE_SIZE << cpu_buffer->buffer->subbuf_order; + meta->meta_struct_len = sizeof(*meta); + meta->nr_subbufs = nr_subbufs; + meta->subbuf_size = cpu_buffer->buffer->subbuf_size + BUF_PAGE_HDR_SIZE; + + rb_update_meta_page(cpu_buffer); +} + +static struct ring_buffer_per_cpu * +rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return ERR_PTR(-EINVAL); + + cpu_buffer = buffer->buffers[cpu]; + + mutex_lock(&cpu_buffer->mapping_lock); + + if (!cpu_buffer->mapped) { + mutex_unlock(&cpu_buffer->mapping_lock); + return ERR_PTR(-ENODEV); + } + + return cpu_buffer; +} + +static void rb_put_mapped_buffer(struct ring_buffer_per_cpu *cpu_buffer) +{ + mutex_unlock(&cpu_buffer->mapping_lock); +} + +/* + * Fast-path for rb_buffer_(un)map(). Called whenever the meta-page doesn't need + * to be set-up or torn-down. + */ +static int __rb_inc_dec_mapped(struct ring_buffer_per_cpu *cpu_buffer, + bool inc) +{ + unsigned long flags; + + lockdep_assert_held(&cpu_buffer->mapping_lock); + + if (inc && cpu_buffer->mapped == UINT_MAX) + return -EBUSY; + + if (WARN_ON(!inc && cpu_buffer->mapped == 0)) + return -EINVAL; + + mutex_lock(&cpu_buffer->buffer->mutex); + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + + if (inc) + cpu_buffer->mapped++; + else + cpu_buffer->mapped--; + + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + mutex_unlock(&cpu_buffer->buffer->mutex); + + return 0; +} + +#define subbuf_page(off, start) \ + virt_to_page((void *)((start) + ((off) << PAGE_SHIFT))) + +#define foreach_subbuf_page(sub_order, start, page) \ + page = subbuf_page(0, (start)); \ + for (int __off = 0; __off < (1 << (sub_order)); \ + __off++, page = subbuf_page(__off, (start))) + +/* + * +--------------+ pgoff == 0 + * | meta page | + * +--------------+ pgoff == 1 + * | 000000000 | + * +--------------+ pgoff == (1 << subbuf_order) + * | subbuffer 0 | + * | | + * +--------------+ pgoff == (2 * (1 << subbuf_order)) + * | subbuffer 1 | + * | | + * ... + */ +static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer, + struct vm_area_struct *vma) +{ + unsigned long nr_subbufs, nr_pages, vma_pages, pgoff = vma->vm_pgoff; + unsigned int subbuf_pages, subbuf_order; + struct page **pages; + int p = 0, s = 0; + int err; + + lockdep_assert_held(&cpu_buffer->mapping_lock); + + subbuf_order = cpu_buffer->buffer->subbuf_order; + subbuf_pages = 1 << subbuf_order; + + if (subbuf_order && pgoff % subbuf_pages) + return -EINVAL; + + nr_subbufs = cpu_buffer->nr_pages + 1; + nr_pages = ((nr_subbufs + 1) << subbuf_order) - pgoff; + + vma_pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT; + if (!vma_pages || vma_pages > nr_pages) + return -EINVAL; + + nr_pages = vma_pages; + + pages = kcalloc(nr_pages, sizeof(*pages), GFP_KERNEL); + if (!pages) + return -ENOMEM; + + if (!pgoff) { + unsigned long meta_page_padding; + + pages[p++] = virt_to_page(cpu_buffer->meta_page); + + /* + * Pad with the zero-page to align the meta-page with the + * sub-buffers. + */ + meta_page_padding = subbuf_pages - 1; + while (meta_page_padding-- && p < nr_pages) + pages[p++] = ZERO_PAGE(0); + } else { + /* Skip the meta-page */ + pgoff -= subbuf_pages; + + s += pgoff / subbuf_pages; + } + + while (s < nr_subbufs && p < nr_pages) { + struct page *page; + + foreach_subbuf_page(subbuf_order, cpu_buffer->subbuf_ids[s], page) { + if (p >= nr_pages) + break; + + pages[p++] = page; + } + s++; + } + + err = vm_insert_pages(vma, vma->vm_start, pages, &nr_pages); + + kfree(pages); + + return err; +} + +int ring_buffer_map(struct trace_buffer *buffer, int cpu, + struct vm_area_struct *vma) +{ + struct ring_buffer_per_cpu *cpu_buffer; + unsigned long flags, *subbuf_ids; + int err = 0; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return -EINVAL; + + cpu_buffer = buffer->buffers[cpu]; + + mutex_lock(&cpu_buffer->mapping_lock); + + if (cpu_buffer->mapped) { + err = __rb_map_vma(cpu_buffer, vma); + if (!err) + err = __rb_inc_dec_mapped(cpu_buffer, true); + mutex_unlock(&cpu_buffer->mapping_lock); + return err; + } + + /* prevent another thread from changing buffer/sub-buffer sizes */ + mutex_lock(&buffer->mutex); + + err = rb_alloc_meta_page(cpu_buffer); + if (err) + goto unlock; + + /* subbuf_ids include the reader while nr_pages does not */ + subbuf_ids = kcalloc(cpu_buffer->nr_pages + 1, sizeof(*subbuf_ids), GFP_KERNEL); + if (!subbuf_ids) { + rb_free_meta_page(cpu_buffer); + err = -ENOMEM; + goto unlock; + } + + atomic_inc(&cpu_buffer->resize_disabled); + + /* + * Lock all readers to block any subbuf swap until the subbuf IDs are + * assigned. + */ + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + rb_setup_ids_meta_page(cpu_buffer, subbuf_ids); + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + + err = __rb_map_vma(cpu_buffer, vma); + if (!err) { + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + cpu_buffer->mapped = 1; + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + } else { + kfree(cpu_buffer->subbuf_ids); + cpu_buffer->subbuf_ids = NULL; + rb_free_meta_page(cpu_buffer); + } +unlock: + mutex_unlock(&buffer->mutex); + mutex_unlock(&cpu_buffer->mapping_lock); + + return err; +} + +int ring_buffer_unmap(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + unsigned long flags; + int err = 0; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return -EINVAL; + + cpu_buffer = buffer->buffers[cpu]; + + mutex_lock(&cpu_buffer->mapping_lock); + + if (!cpu_buffer->mapped) { + err = -ENODEV; + goto out; + } else if (cpu_buffer->mapped > 1) { + __rb_inc_dec_mapped(cpu_buffer, false); + goto out; + } + + mutex_lock(&buffer->mutex); + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); + + cpu_buffer->mapped = 0; + + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + + kfree(cpu_buffer->subbuf_ids); + cpu_buffer->subbuf_ids = NULL; + rb_free_meta_page(cpu_buffer); + atomic_dec(&cpu_buffer->resize_disabled); + + mutex_unlock(&buffer->mutex); +out: + mutex_unlock(&cpu_buffer->mapping_lock); + + return err; +} + +int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + unsigned long reader_size; + unsigned long flags; + + cpu_buffer = rb_get_mapped_buffer(buffer, cpu); + if (IS_ERR(cpu_buffer)) + return (int)PTR_ERR(cpu_buffer); + + raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); +consume: + if (rb_per_cpu_empty(cpu_buffer)) + goto out; + + reader_size = rb_page_size(cpu_buffer->reader_page); + + /* + * There are data to be read on the current reader page, we can + * return to the caller. But before that, we assume the latter will read + * everything. Let's update the kernel reader accordingly. + */ + if (cpu_buffer->reader_page->read < reader_size) { + while (cpu_buffer->reader_page->read < reader_size) + rb_advance_reader(cpu_buffer); + goto out; + } + + if (WARN_ON(!rb_get_reader_page(cpu_buffer))) + goto out; + + goto consume; +out: + /* Some archs do not have data cache coherency between kernel and user-space */ + flush_dcache_folio(virt_to_folio(cpu_buffer->reader_page->page)); + + rb_update_meta_page(cpu_buffer); + + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); + rb_put_mapped_buffer(cpu_buffer); + + return 0; +} + /* * We only allocate new buffers, never free them if the CPU goes down. * If we were to free the buffer, then the user would lose any trace that was in