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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-431bd74f132sm184444555e9.0.2024.11.04.02.45.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 Nov 2024 02:45:21 -0800 (PST) Message-ID: Date: Mon, 4 Nov 2024 11:45:20 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V3 01/16] machine: anon-alloc option From: David Hildenbrand To: Steve Sistare , qemu-devel@nongnu.org Cc: Peter Xu , Fabiano Rosas , Marcel Apfelbaum , Eduardo Habkost , Philippe Mathieu-Daude , Paolo Bonzini , "Daniel P. Berrange" , Markus Armbruster References: <1730468875-249970-1-git-send-email-steven.sistare@oracle.com> <1730468875-249970-2-git-send-email-steven.sistare@oracle.com> <78fa25f1-03dc-400c-a604-998c53e4fbce@redhat.com> Content-Language: en-US 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: <78fa25f1-03dc-400c-a604-998c53e4fbce@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.34, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 04.11.24 11:39, David Hildenbrand wrote: > On 01.11.24 14:47, Steve Sistare wrote: >> Allocate anonymous memory using mmap MAP_ANON or memfd_create depending >> on the value of the anon-alloc machine property. This option applies to >> memory allocated as a side effect of creating various devices. It does >> not apply to memory-backend-objects, whether explicitly specified on >> the command line, or implicitly created by the -m command line option. >> >> The memfd option is intended to support new migration modes, in which the >> memory region can be transferred in place to a new QEMU process, by sending >> the memfd file descriptor to the process. Memory contents are preserved, >> and if the mode also transfers device descriptors, then pages that are >> locked in memory for DMA remain locked. This behavior is a pre-requisite >> for supporting vfio, vdpa, and iommufd devices with the new modes. > > A more portable, non-Linux specific variant of this will be using shm, > similar to backends/hostmem-shm.c. > > Likely we should be using that instead of memfd, or try hiding the > details. See below. > > [...] > >> @@ -69,6 +70,8 @@ >> >> #include "qemu/pmem.h" >> >> +#include "qapi/qapi-types-migration.h" >> +#include "migration/options.h" >> #include "migration/vmstate.h" >> >> #include "qemu/range.h" >> @@ -1849,6 +1852,35 @@ static void ram_block_add(RAMBlock *new_block, Error **errp) >> qemu_mutex_unlock_ramlist(); >> return; >> } >> + >> + } else if (current_machine->anon_alloc == ANON_ALLOC_OPTION_MEMFD && >> + !object_dynamic_cast(new_block->mr->parent_obj.parent, >> + TYPE_MEMORY_BACKEND)) { > > This looks a bit and hackish, and I don't think ram_block_add() is the right > place where this should be. It should likely happen in the caller. > > We already do have two ways of allocating "shared anonymous memory": > > (1) memory-backend-ram,share=on > (2) memory-backend-shm > > (2) gives us an fd as it uses shm_open(), (1) doesn't give us an fd as it > uses MAP_ANON|MAP_SHARED. (1) is really only a corner case use case [1]. > > [there is also Linux specific memfd, which gives us more flexibility with > hugetlb etc, but for the purpose here shm should likely be sufficient?] > > So why not make (1) behave like (2) and move that handling into > qemu_ram_alloc_internal(), from where we can easily enable it using a > new RMA_SHARED flag? So as a first step, something like: > > From 4b7b760c6e54cf05addca6728edc19adbec1588a Mon Sep 17 00:00:00 2001 > From: David Hildenbrand > Date: Mon, 4 Nov 2024 11:29:22 +0100 > Subject: [PATCH] tmp > > Signed-off-by: David Hildenbrand > --- > backends/hostmem-shm.c | 56 ++++---------------------------- > system/physmem.c | 73 ++++++++++++++++++++++++++++++++++++++++-- > 2 files changed, 76 insertions(+), 53 deletions(-) > > diff --git a/backends/hostmem-shm.c b/backends/hostmem-shm.c > index 374edc3db8..0f33b35e9c 100644 > --- a/backends/hostmem-shm.c > +++ b/backends/hostmem-shm.c > @@ -25,11 +25,8 @@ struct HostMemoryBackendShm { > static bool > shm_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) > { > - g_autoptr(GString) shm_name = g_string_new(NULL); > - g_autofree char *backend_name = NULL; > + g_autofree char *name = NULL; > uint32_t ram_flags; > - int fd, oflag; > - mode_t mode; > > if (!backend->size) { > error_setg(errp, "can't create shm backend with size 0"); > @@ -41,54 +38,13 @@ shm_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) > return false; > } > > - /* > - * Let's use `mode = 0` because we don't want other processes to open our > - * memory unless we share the file descriptor with them. > - */ > - mode = 0; > - oflag = O_RDWR | O_CREAT | O_EXCL; > - backend_name = host_memory_backend_get_name(backend); > - > - /* > - * Some operating systems allow creating anonymous POSIX shared memory > - * objects (e.g. FreeBSD provides the SHM_ANON constant), but this is not > - * defined by POSIX, so let's create a unique name. > - * > - * From Linux's shm_open(3) man-page: > - * For portable use, a shared memory object should be identified > - * by a name of the form /somename;" > - */ > - g_string_printf(shm_name, "/qemu-" FMT_pid "-shm-%s", getpid(), > - backend_name); > - > - fd = shm_open(shm_name->str, oflag, mode); > - if (fd < 0) { > - error_setg_errno(errp, errno, > - "failed to create POSIX shared memory"); > - return false; > - } > - > - /* > - * We have the file descriptor, so we no longer need to expose the > - * POSIX shared memory object. However it will remain allocated as long as > - * there are file descriptors pointing to it. > - */ > - shm_unlink(shm_name->str); > - > - if (ftruncate(fd, backend->size) == -1) { > - error_setg_errno(errp, errno, > - "failed to resize POSIX shared memory to %" PRIu64, > - backend->size); > - close(fd); > - return false; > - } > - > + /* Let's do the same as memory-backend-ram,share=on would do. */ > + name = host_memory_backend_get_name(backend); > ram_flags = RAM_SHARED; > ram_flags |= backend->reserve ? 0 : RAM_NORESERVE; > - > - return memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend), > - backend_name, backend->size, > - ram_flags, fd, 0, errp); > + return memory_region_init_ram_flags_nomigrate(&backend->mr, OBJECT(backend), > + name, backend->size, > + ram_flags, errp); > } > > static void > diff --git a/system/physmem.c b/system/physmem.c > index dc1db3a384..4d331b3828 100644 > --- a/system/physmem.c > +++ b/system/physmem.c > @@ -2057,6 +2057,59 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr, > } > #endif > > +static int qemu_shm_alloc(size_t size, Error **errp) > +{ > + g_autoptr(GString) shm_name = g_string_new(NULL); > + int fd, oflag, cur_sequence; > + static int sequence; > + mode_t mode; > + > + cur_sequence = qatomic_fetch_inc(&sequence); > + > + /* > + * Let's use `mode = 0` because we don't want other processes to open our > + * memory unless we share the file descriptor with them. > + */ > + mode = 0; > + oflag = O_RDWR | O_CREAT | O_EXCL; > + > + /* > + * Some operating systems allow creating anonymous POSIX shared memory > + * objects (e.g. FreeBSD provides the SHM_ANON constant), but this is not > + * defined by POSIX, so let's create a unique name. > + * > + * From Linux's shm_open(3) man-page: > + * For portable use, a shared memory object should be identified > + * by a name of the form /somename;" > + */ > + g_string_printf(shm_name, "/qemu-" FMT_pid "-shm-%d", getpid(), > + cur_sequence); > + > + fd = shm_open(shm_name->str, oflag, mode); > + if (fd < 0) { > + error_setg_errno(errp, errno, > + "failed to create POSIX shared memory"); > + return false; > + } > + > + /* > + * We have the file descriptor, so we no longer need to expose the > + * POSIX shared memory object. However it will remain allocated as long as > + * there are file descriptors pointing to it. > + */ > + shm_unlink(shm_name->str); > + > + if (ftruncate(fd, size) == -1) { > + error_setg_errno(errp, errno, > + "failed to resize POSIX shared memory to %" PRIu64, > + size); > + close(fd); > + return false; > + } > + > + return fd; > +} > + > static > RAMBlock *qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size, > void (*resized)(const char*, > @@ -2084,12 +2137,26 @@ RAMBlock *qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size, > new_block->used_length = size; > new_block->max_length = max_size; > assert(max_size >= size); > - new_block->fd = -1; > + > new_block->guest_memfd = -1; > new_block->page_size = qemu_real_host_page_size(); > - new_block->host = host; > new_block->flags = ram_flags; > - ram_block_add(new_block, &local_err); > + new_block->host = host; > + > + if ((ram_flags & RAM_PREALLOC) || !(ram_flags & RAM_SHARED)) { > + new_block->fd = -1; > + } else { > + /* > + * We want anonymous shared memory, similar to MAP_SHARED|MAP_ANON; but > + * some users want the fd. So let's allocate shm explicitly, which will > + * give us the fd. > + */ > + assert(!host); > + new_block->fd = qemu_shm_alloc(new_block->max_length, &local_err); Note: completely untested. Likely a file_ram_alloc() call is missing here. -- Cheers, David / dhildenb