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([2a01:cb19:9004:d500:837f:93fd:c85e:5b97]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-390e485d773sm4495663f8f.81.2025.02.28.00.53.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Feb 2025 00:53:13 -0800 (PST) Message-ID: <800e20f0-8568-40f0-ba40-0026f14f5467@redhat.com> Date: Fri, 28 Feb 2025 09:53:12 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 34/36] vfio/migration: Max in-flight VFIO device state buffer count limit To: "Maciej S. Szmigiero" Cc: Alex Williamson , Eric Blake , Peter Xu , Fabiano Rosas , Markus Armbruster , =?UTF-8?Q?Daniel_P_=2E_Berrang=C3=A9?= , Avihai Horon , Joao Martins , qemu-devel@nongnu.org References: <719b309bb7bc13542d14e6ce0026cb9bb67e9f31.1739994627.git.maciej.szmigiero@oracle.com> <11ecf7fb-55f6-4606-b635-e53dbcc71dbc@redhat.com> Content-Language: en-US, fr From: =?UTF-8?Q?C=C3=A9dric_Le_Goater?= Autocrypt: addr=clg@redhat.com; keydata= xsFNBFu8o3UBEADP+oJVJaWm5vzZa/iLgpBAuzxSmNYhURZH+guITvSySk30YWfLYGBWQgeo 8NzNXBY3cH7JX3/a0jzmhDc0U61qFxVgrPqs1PQOjp7yRSFuDAnjtRqNvWkvlnRWLFq4+U5t yzYe4SFMjFb6Oc0xkQmaK2flmiJNnnxPttYwKBPd98WfXMmjwAv7QfwW+OL3VlTPADgzkcqj 53bfZ4VblAQrq6Ctbtu7JuUGAxSIL3XqeQlAwwLTfFGrmpY7MroE7n9Rl+hy/kuIrb/TO8n0 ZxYXvvhT7OmRKvbYuc5Jze6o7op/bJHlufY+AquYQ4dPxjPPVUT/DLiUYJ3oVBWFYNbzfOrV RxEwNuRbycttMiZWxgflsQoHF06q/2l4ttS3zsV4TDZudMq0TbCH/uJFPFsbHUN91qwwaN/+ gy1j7o6aWMz+Ib3O9dK2M/j/O/Ube95mdCqN4N/uSnDlca3YDEWrV9jO1mUS/ndOkjxa34ia 70FjwiSQAsyIwqbRO3CGmiOJqDa9qNvd2TJgAaS2WCw/TlBALjVQ7AyoPEoBPj31K74Wc4GS Rm+FSch32ei61yFu6ACdZ12i5Edt+To+hkElzjt6db/UgRUeKfzlMB7PodK7o8NBD8outJGS tsL2GRX24QvvBuusJdMiLGpNz3uqyqwzC5w0Fd34E6G94806fwARAQABzSJDw6lkcmljIExl IEdvYXRlciA8Y2xnQHJlZGhhdC5jb20+wsGRBBMBCAA7FiEEoPZlSPBIlev+awtgUaNDx8/7 7KEFAmTLlVECGwMFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgkQUaNDx8/77KG0eg// S0zIzTcxkrwJ/9XgdcvVTnXLVF9V4/tZPfB7sCp8rpDCEseU6O0TkOVFoGWM39sEMiQBSvyY lHrP7p7E/JYQNNLh441MfaX8RJ5Ul3btluLapm8oHp/vbHKV2IhLcpNCfAqaQKdfk8yazYhh EdxTBlzxPcu+78uE5fF4wusmtutK0JG0sAgq0mHFZX7qKG6LIbdLdaQalZ8CCFMKUhLptW71 xe+aNrn7hScBoOj2kTDRgf9CE7svmjGToJzUxgeh9mIkxAxTu7XU+8lmL28j2L5uNuDOq9vl hM30OT+pfHmyPLtLK8+GXfFDxjea5hZLF+2yolE/ATQFt9AmOmXC+YayrcO2ZvdnKExZS1o8 VUKpZgRnkwMUUReaF/mTauRQGLuS4lDcI4DrARPyLGNbvYlpmJWnGRWCDguQ/LBPpbG7djoy k3NlvoeA757c4DgCzggViqLm0Bae320qEc6z9o0X0ePqSU2f7vcuWN49Uhox5kM5L86DzjEQ RHXndoJkeL8LmHx8DM+kx4aZt0zVfCHwmKTkSTQoAQakLpLte7tWXIio9ZKhUGPv/eHxXEoS 0rOOAZ6np1U/xNR82QbF9qr9TrTVI3GtVe7Vxmff+qoSAxJiZQCo5kt0YlWwti2fFI4xvkOi V7lyhOA3+/3oRKpZYQ86Frlo61HU3r6d9wzOwU0EW7yjdQEQALyDNNMw/08/fsyWEWjfqVhW pOOrX2h+z4q0lOHkjxi/FRIRLfXeZjFfNQNLSoL8j1y2rQOs1j1g+NV3K5hrZYYcMs0xhmrZ KXAHjjDx7FW3sG3jcGjFW5Xk4olTrZwFsZVUcP8XZlArLmkAX3UyrrXEWPSBJCXxDIW1hzwp bV/nVbo/K9XBptT/wPd+RPiOTIIRptjypGY+S23HYBDND3mtfTz/uY0Jytaio9GETj+fFis6 TxFjjbZNUxKpwftu/4RimZ7qL+uM1rG1lLWc9SPtFxRQ8uLvLOUFB1AqHixBcx7LIXSKZEFU CSLB2AE4wXQkJbApye48qnZ09zc929df5gU6hjgqV9Gk1rIfHxvTsYltA1jWalySEScmr0iS YBZjw8Nbd7SxeomAxzBv2l1Fk8fPzR7M616dtb3Z3HLjyvwAwxtfGD7VnvINPbzyibbe9c6g LxYCr23c2Ry0UfFXh6UKD83d5ybqnXrEJ5n/t1+TLGCYGzF2erVYGkQrReJe8Mld3iGVldB7 JhuAU1+d88NS3aBpNF6TbGXqlXGF6Yua6n1cOY2Yb4lO/mDKgjXd3aviqlwVlodC8AwI0Sdu jWryzL5/AGEU2sIDQCHuv1QgzmKwhE58d475KdVX/3Vt5I9kTXpvEpfW18TjlFkdHGESM/Jx IqVsqvhAJkalABEBAAHCwV8EGAECAAkFAlu8o3UCGwwACgkQUaNDx8/77KEhwg//WqVopd5k 8hQb9VVdk6RQOCTfo6wHhEqgjbXQGlaxKHoXywEQBi8eULbeMQf5l4+tHJWBxswQ93IHBQjK yKyNr4FXseUI5O20XVNYDJZUrhA4yn0e/Af0IX25d94HXQ5sMTWr1qlSK6Zu79lbH3R57w9j hQm9emQEp785ui3A5U2Lqp6nWYWXz0eUZ0Tad2zC71Gg9VazU9MXyWn749s0nXbVLcLS0yop s302Gf3ZmtgfXTX/W+M25hiVRRKCH88yr6it+OMJBUndQVAA/fE9hYom6t/zqA248j0QAV/p LHH3hSirE1mv+7jpQnhMvatrwUpeXrOiEw1nHzWCqOJUZ4SY+HmGFW0YirWV2mYKoaGO2YBU wYF7O9TI3GEEgRMBIRT98fHa0NPwtlTktVISl73LpgVscdW8yg9Gc82oe8FzU1uHjU8b10lU XOMHpqDDEV9//r4ZhkKZ9C4O+YZcTFu+mvAY3GlqivBNkmYsHYSlFsbxc37E1HpTEaSWsGfA HQoPn9qrDJgsgcbBVc1gkUT6hnxShKPp4PlsZVMNjvPAnr5TEBgHkk54HQRhhwcYv1T2QumQ izDiU6iOrUzBThaMhZO3i927SG2DwWDVzZltKrCMD1aMPvb3NU8FOYRhNmIFR3fcalYr+9gD uVKe8BVz4atMOoktmt0GWTOC8P4= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=clg@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.438, 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_H5=0.001, RCVD_IN_MSPIKE_WL=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 2/27/25 23:01, Maciej S. Szmigiero wrote: > On 27.02.2025 07:48, Cédric Le Goater wrote: >> On 2/19/25 21:34, Maciej S. Szmigiero wrote: >>> From: "Maciej S. Szmigiero" >>> >>> Allow capping the maximum count of in-flight VFIO device state buffers >>> queued at the destination, otherwise a malicious QEMU source could >>> theoretically cause the target QEMU to allocate unlimited amounts of memory >>> for buffers-in-flight. >>> >>> Since this is not expected to be a realistic threat in most of VFIO live >>> migration use cases and the right value depends on the particular setup >>> disable the limit by default by setting it to UINT64_MAX. >>> >>> Signed-off-by: Maciej S. Szmigiero >>> --- >>>   hw/vfio/migration-multifd.c   | 14 ++++++++++++++ >>>   hw/vfio/pci.c                 |  2 ++ >>>   include/hw/vfio/vfio-common.h |  1 + >>>   3 files changed, 17 insertions(+) >>> >>> diff --git a/hw/vfio/migration-multifd.c b/hw/vfio/migration-multifd.c >>> index 18a5ff964a37..04aa3f4a6596 100644 >>> --- a/hw/vfio/migration-multifd.c >>> +++ b/hw/vfio/migration-multifd.c >>> @@ -53,6 +53,7 @@ typedef struct VFIOMultifd { >>>       QemuMutex load_bufs_mutex; /* Lock order: this lock -> BQL */ >>>       uint32_t load_buf_idx; >>>       uint32_t load_buf_idx_last; >>> +    uint32_t load_buf_queued_pending_buffers; >>>   } VFIOMultifd; >>>   static void vfio_state_buffer_clear(gpointer data) >>> @@ -121,6 +122,15 @@ static bool vfio_load_state_buffer_insert(VFIODevice *vbasedev, >>>       assert(packet->idx >= multifd->load_buf_idx); >>> +    multifd->load_buf_queued_pending_buffers++; >>> +    if (multifd->load_buf_queued_pending_buffers > >>> +        vbasedev->migration_max_queued_buffers) { >>> +        error_setg(errp, >>> +                   "queuing state buffer %" PRIu32 " would exceed the max of %" PRIu64, >>> +                   packet->idx, vbasedev->migration_max_queued_buffers); >>> +        return false; >>> +    } >>> + >>>       lb->data = g_memdup2(&packet->data, packet_total_size - sizeof(*packet)); >>>       lb->len = packet_total_size - sizeof(*packet); >>>       lb->is_present = true; >>> @@ -374,6 +384,9 @@ static bool vfio_load_bufs_thread(void *opaque, bool *should_quit, Error **errp) >>>               goto ret_signal; >>>           } >>> +        assert(multifd->load_buf_queued_pending_buffers > 0); >>> +        multifd->load_buf_queued_pending_buffers--; >>> + >>>           if (multifd->load_buf_idx == multifd->load_buf_idx_last - 1) { >>>               trace_vfio_load_state_device_buffer_end(vbasedev->name); >>>           } >>> @@ -408,6 +421,7 @@ VFIOMultifd *vfio_multifd_new(void) >>>       multifd->load_buf_idx = 0; >>>       multifd->load_buf_idx_last = UINT32_MAX; >>> +    multifd->load_buf_queued_pending_buffers = 0; >>>       qemu_cond_init(&multifd->load_bufs_buffer_ready_cond); >>>       multifd->load_bufs_thread_running = false; >>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c >>> index 9111805ae06c..247418f0fce2 100644 >>> --- a/hw/vfio/pci.c >>> +++ b/hw/vfio/pci.c >>> @@ -3383,6 +3383,8 @@ static const Property vfio_pci_dev_properties[] = { >>>                   vbasedev.migration_multifd_transfer, >>>                   qdev_prop_on_off_auto_mutable, OnOffAuto, >>>                   .set_default = true, .defval.i = ON_OFF_AUTO_AUTO), >>> +    DEFINE_PROP_UINT64("x-migration-max-queued-buffers", VFIOPCIDevice, >>> +                       vbasedev.migration_max_queued_buffers, UINT64_MAX), >> >> UINT64_MAX doesn't make sense to me. What would be a reasonable value ? > > It's the value that effectively disables this limit. > >> Have you monitored the max ? Should we collect some statistics on this >> value and raise a warning if a high water mark is reached ? I think >> this would more useful. > > It's an additional mechanism, which is not expected to be necessary > in most of real-world setups, hence it's disabled by default: >> Since this is not expected to be a realistic threat in most of VFIO live >> migration use cases and the right value depends on the particular setup >> disable the limit by default by setting it to UINT64_MAX. > > The minimum value that works with particular setup depends on number of > multifd channels, probably also the number of NIC queues, etc. so it's > not something we should propose hard default to - unless it's a very > high default like 100 buffers, but then why have it set by default?. > > IMHO setting it to UINT64_MAX clearly shows that it is disabled by > default since it obviously couldn't be set higher. This doesn't convince me that we should take this patch in QEMU 10.0. Please keep for now. We will decide in v6. >>>       DEFINE_PROP_BOOL("migration-events", VFIOPCIDevice, >>>                        vbasedev.migration_events, false), >>>       DEFINE_PROP_BOOL("x-no-mmap", VFIOPCIDevice, vbasedev.no_mmap, false), >> >> >> Please add property documentation in vfio_pci_dev_class_init() >> > > I'm not sure what you mean by that, vfio_pci_dev_class_init() doesn't > contain any documentation or even references to either > x-migration-max-queued-buffers or x-migration-multifd-transfer: Indeed :/ I am trying to fix documentation here : https://lore.kernel.org/qemu-devel/20250217173455.449983-1-clg@redhat.com/ Please do something similar. I will polish the edges when merging if necessary. Overall, we should improve VFIO documentation, migration is one sub-feature among many. Thanks, C. >> static void vfio_pci_dev_class_init(ObjectClass *klass, void *data) >> { >>     DeviceClass *dc = DEVICE_CLASS(klass); >>     PCIDeviceClass *pdc = PCI_DEVICE_CLASS(klass); >> >>     device_class_set_legacy_reset(dc, vfio_pci_reset); >>     device_class_set_props(dc, vfio_pci_dev_properties); >> #ifdef CONFIG_IOMMUFD >>     object_class_property_add_str(klass, "fd", NULL, vfio_pci_set_fd); >> #endif >>     dc->desc = "VFIO-based PCI device assignment"; >>     set_bit(DEVICE_CATEGORY_MISC, dc->categories); >>     pdc->realize = vfio_realize; >>     pdc->exit = vfio_exitfn; >>     pdc->config_read = vfio_pci_read_config; >>     pdc->config_write = vfio_pci_write_config; >> } > > >> Thanks, >> >> C. > > Thanks, > Maciej >