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[2003:cb:c71e:bf00:eba1:3ab9:ab0f:d676]) by smtp.gmail.com with ESMTPSA id n12-20020adfe34c000000b00343d6c7240fsm1288517wrj.35.2024.05.02.06.30.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 May 2024 06:30:33 -0700 (PDT) Message-ID: <78e20e98-bdfc-4d7b-a59c-988b81fcc58b@redhat.com> Date: Thu, 2 May 2024 15:30:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v22 2/5] ring-buffer: Introducing ring-buffer mapping functions To: Vincent Donnefort , 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, rppt@kernel.org, linux-mm@kvack.org References: <20240430111354.637356-1-vdonnefort@google.com> <20240430111354.637356-3-vdonnefort@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20240430111354.637356-3-vdonnefort@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 462F61C0014 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: x3e66bx8jmasf84h1tzh54wzasqqmnii X-HE-Tag: 1714656638-97781 X-HE-Meta: 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 z3YVyKsb /710uCIjoIkngzcqBSuVyzI92wCG45AprOENFsL5Qhrkpa0lCbwGMczmNA5TBJeiLnLl0904LsXhrmE3Zx+HqC0Q5lbLRjj/m+fYD0cmk5w+lLOyQeOgTcQcfQlrK8hJSg8Jjh+KwoqCTBxeovY9UbE7HI3ZaDDW+yY29xQxfwSslEsfbYzbG9s+kGz1nBgIJBX937vYpEbGiRv/5a7AoERWbioxtLWX9sbPj2me2gbh0ymDZYejrT5VVcH3q+7KGezLX4NmsVYXw1ACiOLthibVFp8r48URgns2Jo6c8QBhQRa1Ik6ijtflH3Gqlo2Xo2mlqTTw4GTmZDk4NI9YxLRLK7GrH/qA76ujBIZ/qXLNo2aTzthT0u7fAm7Kz3os6nJNk9n6Th4CyhEiU9cUUFddaJ5Tr0pyPFAjbe8m709MEVYIRj1C/yaT6HpvpB4wosEHOjuTmUBxr1Z+ba5fPsAgi45tvborZIWQ9y9DI7DxCZfocUegZxDMnKW8rqbl+JaLzNcXVfasUUolMa0ketF8o3Oufb1p5P6pV+/y+vAQrqOYYvKXNgVaRf806ToVhW8Cr 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: On 30.04.24 13:13, 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 [...] > +/* > + * +--------------+ pgoff == 0 > + * | meta page | > + * +--------------+ pgoff == 1 > + * | subbuffer 0 | > + * | | > + * +--------------+ pgoff == (1 + (1 << subbuf_order)) > + * | subbuffer 1 | > + * | | > + * ... > + */ > +#ifdef CONFIG_MMU > +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; > + > + /* Refuse MP_PRIVATE or writable mappings */ > + if (vma->vm_flags & VM_WRITE || vma->vm_flags & VM_EXEC || > + !(vma->vm_flags & VM_MAYSHARE)) > + return -EPERM; > + > + /* > + * Make sure the mapping cannot become writable later. Also tell the VM > + * to not touch these pages (VM_DONTCOPY | VM_DONTEXPAND). Finally, > + * prevent migration, GUP and dump (VM_IO). > + */ > + vm_flags_mod(vma, VM_DONTCOPY | VM_DONTEXPAND | VM_IO, VM_MAYWRITE); > + > + lockdep_assert_held(&cpu_buffer->mapping_lock); > + > + subbuf_order = cpu_buffer->buffer->subbuf_order; > + subbuf_pages = 1 << subbuf_order; > + > + nr_subbufs = cpu_buffer->nr_pages + 1; /* + reader-subbuf */ > + nr_pages = ((nr_subbufs) << subbuf_order) - pgoff + 1; /* + meta-page */ > + > + 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) { > + pages[p++] = virt_to_page(cpu_buffer->meta_page); > + > + /* > + * TODO: Align sub-buffers on their size, once > + * vm_insert_pages() supports the zero-page. > + */ > + } else { > + /* Skip the meta-page */ > + pgoff--; > + > + if (pgoff % subbuf_pages) { > + err = -EINVAL; > + goto out; > + } > + > + s += pgoff / subbuf_pages; > + } > + > + while (s < nr_subbufs && p < nr_pages) { > + struct page *page = virt_to_page(cpu_buffer->subbuf_ids[s]); > + int off = 0; > + > + for (; off < (1 << (subbuf_order)); off++, page++) { > + if (p >= nr_pages) > + break; > + > + pages[p++] = page; > + } > + s++; > + } > + > + err = vm_insert_pages(vma, vma->vm_start, pages, &nr_pages); Nit: I did not immediately understand if we could end here with p < nr_pages (IOW, pages[] not completely filled). One source of confusion is the "s < nr_subbufs" check in the while loop: why is "p < nr_pages" insufficient? For the MM bits: Acked-by: David Hildenbrand -- Cheers, David / dhildenb