From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id BCF0AC4345F for ; Mon, 22 Apr 2024 18:20:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1E99D6B008A; Mon, 22 Apr 2024 14:20:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 199FA6B008C; Mon, 22 Apr 2024 14:20:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 013896B0092; Mon, 22 Apr 2024 14:20:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id CEE166B008A for ; Mon, 22 Apr 2024 14:20:56 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 50B604019D for ; Mon, 22 Apr 2024 18:20:56 +0000 (UTC) X-FDA: 82037984112.18.FCAB07C Received: from mail-wm1-f53.google.com (mail-wm1-f53.google.com [209.85.128.53]) by imf30.hostedemail.com (Postfix) with ESMTP id 49F9980014 for ; Mon, 22 Apr 2024 18:20:54 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=dVnfZV1S; spf=pass (imf30.hostedemail.com: domain of vdonnefort@google.com designates 209.85.128.53 as permitted sender) smtp.mailfrom=vdonnefort@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1713810054; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=wZjtUG1a/GbcMMV+5gh6qXmWbPxih3XxuMfN7gw2rBM=; b=to9f2oohgfk7Qxm6AU1xy7TG+iSgF90YO+W1KLt2T2nnzrcvZIqveRJYTzXFOygv5wgEZF EdsMf065aS8/2w2cZhReY2v0diHUwUHMopjSSyEon1mTJTsWPjxxgLlDePedXrvU7unLnk wTQD6CX30so+LG079tPvZ1lG0giP54Q= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1713810054; a=rsa-sha256; cv=none; b=xISY9J+HKbv/7oWehV4RvzR26Zff6Dv1VTtUteAJQoPRbN5PlApwfiu3QGGJjIqwRv00qn qm/Vd2Y4D5Uz0AkID28muzHTR6/OlXgWsojQixEhRcj1QRemJyram3Qs8qdsi/6rRKTryU +t9i6WITU3Pi+iMB1XItvlTEQhgdhkA= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=dVnfZV1S; spf=pass (imf30.hostedemail.com: domain of vdonnefort@google.com designates 209.85.128.53 as permitted sender) smtp.mailfrom=vdonnefort@google.com; dmarc=pass (policy=reject) header.from=google.com Received: by mail-wm1-f53.google.com with SMTP id 5b1f17b1804b1-41a523e2888so9528705e9.1 for ; Mon, 22 Apr 2024 11:20:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1713810053; x=1714414853; darn=kvack.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=wZjtUG1a/GbcMMV+5gh6qXmWbPxih3XxuMfN7gw2rBM=; b=dVnfZV1SiN39aAmHzEx0ZQv3EL0maVvKQ9l1u976Eg6UuI+KCauIRHh3YxgCp3PDFc bhSpAzTz6bbf2VefhyT7NpklWBVkyUy2aLyOX0sc7kYaQ0wAblMBVcPg5HZ0MtYIlNRn aiFfUxcVdX+7dElhjgZHAP002F+Isr95P3toVmPWun9jJCUYpXQgR0Ni4xlvbO2fH3Gd 6xPhoOTVQMmEVXC1jEGWqQGGztC5xyWCn0gcoOlDoAE+pd+SnZRrxWRjmZ0l8IsDgosl bJMRLf3GCDgPlWhIluBEemKoFl1KSLuvoHcAj7iMd/Igv3VQmSUva1xDSK1cOwS3nN5F 2iTg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1713810053; x=1714414853; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=wZjtUG1a/GbcMMV+5gh6qXmWbPxih3XxuMfN7gw2rBM=; b=rWEpurESFn6Em3RfqIWgiE7QNkGl4ZqEF0bCkh1WU4FypXf6DJhYYmxr9GsQjQiDxl VWn9InAqboYZvroCXg+jiUXnzDs695fEcO33lX/DJE1MEWUfuYgilcEmaEasqtaJBm8W JmdxcDbyIC+UVf8dDbKbE95sTsH7TWOIMV7Wc/rdiR/owuyLE/JTLRvBjn0VHPA+gfMs 1GWAAc4dq3uH1vft2HLAy9vz50SLCsb1/QnAoe3+YVlaRke/BnfjfYfrJk89IQOYgM2n DxFvV0bqTXJaUt3RwdRtfNztbM3NW3DBRI723E4CMCTjbip1DC3tYF46fZvUQ3mOHqLg n9LA== X-Forwarded-Encrypted: i=1; AJvYcCWRixjMX4eN3LV1kjr0Yxlirq7vRPvIAfa0k5cXlc8y7eRs4+Z/SZkSE03k5fdGSUf1vRxyrD+WkpzstLOmldR5W7g= X-Gm-Message-State: AOJu0YwMkIHulkP7qFxUPnxP4oiFG21omMPnyVGlSTWKCl877N+jl6AE vB46iLWwuYZ/Te2jsE+9HQCfg+t9ov2gT3zVeZdhaQqLhdZCYG/vqZp3yiWSbA== X-Google-Smtp-Source: AGHT+IFigyt7KOsWRb7b2XYfKCpySPBXaDuxvFhCB5q8z7NpeV7MdkMOxGA/MzqqiUk+HpelgcScvQ== X-Received: by 2002:a05:600c:1988:b0:418:bbb6:95b3 with SMTP id t8-20020a05600c198800b00418bbb695b3mr8286466wmq.0.1713810052535; Mon, 22 Apr 2024 11:20:52 -0700 (PDT) Received: from google.com (88.140.78.34.bc.googleusercontent.com. [34.78.140.88]) by smtp.gmail.com with ESMTPSA id e15-20020a05600c218f00b004146e58cc35sm20744546wme.46.2024.04.22.11.20.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Apr 2024 11:20:52 -0700 (PDT) Date: Mon, 22 Apr 2024 19:20:48 +0100 From: Vincent Donnefort To: David Hildenbrand Cc: rostedt@goodmis.org, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com, kernel-team@android.com, rdunlap@infradead.org, linux-mm@kvack.org Subject: Re: [PATCH v20 2/5] ring-buffer: Introducing ring-buffer mapping functions Message-ID: References: <20240406173649.3210836-1-vdonnefort@google.com> <20240406173649.3210836-3-vdonnefort@google.com> <9c553dae-5395-4ec9-b41c-a4decc37acf2@redhat.com> <06c6b023-6cdc-430d-be0b-086fd6453aeb@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <06c6b023-6cdc-430d-be0b-086fd6453aeb@redhat.com> X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 49F9980014 X-Stat-Signature: tccc94ydnfuyccue9f4mm9owzf79ptxu X-HE-Tag: 1713810054-413895 X-HE-Meta: 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 nkwF++TC fOpS7VLyEldSSvZJo93KOHF5+ZxqGigOJGpHudrrBE0d6oXj4f1Nv4A4/zlP7WOJJS8HuAwRQtBQd5b8R8DU7gMtKwbBakGT/t5FPNQRFIWuSbLzA8KysVDXN41YBuEY5QGoDfG4liqr6vdzci6SRvwT6j1Aam3orNsYBSWnElIYZdZQTzmnJs9iq7ELZbQ/801kR+GaNn863BhlDLDMcWmpueTtG6+Wx8EreQuVN4yLne+wSGaHjJuy9dVNyR3tNURb09G3GsHLL3tfDEziJRYt96vukfuk86p+ixyM8UJ7FhWp+SJNW8rgKntz5Lub/cUeWbPV+qvmu9uHA+Plm7hb9qT9KuLRxD3tnaAQB9neOrPie5jLu+wbJYSNh0UtzEvsxQtSM+TjmV1Df6InjlKKmjVIdt/IjpQZEzYKip1LHUxc8luDwS5gJy7rU1yE9w2/c 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: Hi David, Thanks for having a look, very much appreciated! On Mon, Apr 22, 2024 at 11:27:11AM +0200, David Hildenbrand wrote: > On 19.04.24 20:25, David Hildenbrand wrote: > > On 06.04.24 19:36, Vincent Donnefort wrote: > > > 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); > > > > Using the shared zeropage in a MAP_SHARED mapping that is neither VM_IO > > nor VM_PFNMAP can be problematic. So we really need patch #3 logic to > > use VM_PFNMAP. > > > > It would be cleaner/more obvious if these VMA flag setting would reside tracing_buffers_mmap() sets both VM_IO and VM_PFNMAP. But, yeah as vma is already passed to ring_buffer_map(). The flags could be set here as this function is what sets the requirements really. > > here, if possible. > > > > > + } 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); > > > > I think Linus suggested it ("avoid all the sub-page ref-counts entirely > > by using VM_PFNMAP, and use vm_insert_pages()"), but ... > > vm_insert_pages() will: > > * Mess with mapcounts > > * Mess with refcounts > > > > See > > insert_pages()->insert_page_in_batch_locked()->insert_page_into_pte_locked(). > > > > So we'll mess with the mapcount and refcount of the shared zeropage ... > > hmmmm > > > > If I am not wrong, vm_normal_page() would not return the shared zeropage > > in case we don't have CONFIG_ARCH_HAS_PTE_SPECIAL ... so > > unmap()->...->zap_present_ptes() would not decrement the refcount and we > > could overflow it. ... we also shouldn't ever mess with the mapcount of > > the shared zeropage in the first place. > > > > vm_insert_page() is clearer on that: "This allows drivers to insert > > individual pages they've allocated into a user vma". You didn't allocate > > the shared zeropage. > > > > I'm wondering if we even expect VM_MIXEDMAP and VM_PFNMAP to be set at > > the same time? vm_insert_pages() would BUG_ON in case VM_PFNMAP is > > already set and it would set VM_MIXEDMAP ... similarly > > vmf_insert_pfn_prot() would not be happy about that at all ... > > > > BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) == > > (VM_PFNMAP|VM_MIXEDMAP)); > > > > ... remap_pfn_range() is used by io_uring_mmap for a similar purpose. > > But it only supports a single PFN range at a time and requires the > > caller to handle refcounting of pages. > > > > It's getting late in Germany, so I might be missing something; but using > > the shared zeropage here might be a problem. > > > > I was just about to write code to cleanly support vm_insert_pages() to > consume zeropages ... when I started to wonder about something else: Alternatively, we could at the moment allocate a meta-page of the same size than the subbufs? (of course the downside is to waste a bit of memory) > > > + if (vma->vm_flags & VM_WRITE || vma->vm_flags & VM_EXEC || > + !(vma->vm_flags & VM_MAYSHARE)) > + return -EPERM; > + > > You disallow writable mappings. But what about using mprotect() afterwards > to allow for write permissions? > > Likely you'd want to remove VM_MAYWRITE from the flags, otherwise mprotect() > might alter succeed. The vm_flags_mod below is clearing VM_MAYWRITE already. Isn't it enough? > > -- > Cheers, > > David / dhildenb >