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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1772643178; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=hon6YFACQydjiVC2MLBH4P+JHfOzlsYj8EtkcwJKskg=; b=aWhJQMRZ+N3RHvO7YKnbgQ0GLbA66laszmJy5kD0oVB064XL/VhFhtNlIYcQhl/jIlL4E/ iGy3/EFUAIlxflSE8xfY/fnkNhhXHypvnFJ7rGJJbf8sGJJ7v+gzEDr3u1YBIdHD+O5qpw bhB53Int8610lnYGO/V09l21zM8EKus= X-MC-Unique: _fb43jOkPLGvfB81hvDKPg-1 X-Mimecast-MFC-AGG-ID: _fb43jOkPLGvfB81hvDKPg_1772643173 From: Albert Esteve To: qemu-devel@nongnu.org Cc: mst@redhat.com, Stefano Garzarella , manos.pitsidianakis@linaro.org, slp@redhat.com, =?UTF-8?q?Alex=20Benn=C3=A9e?= , stefanha@redhat.com, stevensd@chromium.org, Laurent Vivier , jasowang@redhat.com, Peter Xu , hi@alyssa.is, Pierrick Bouvier , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Fabiano Rosas , dbassey@redhat.com, Paolo Bonzini Subject: [PATCH v14 3/7] vhost_user.rst: Add SHMEM_MAP/_UNMAP to spec Date: Wed, 4 Mar 2026 17:52:19 +0100 Message-ID: <20260304165223.2166175-4-aesteve@redhat.com> In-Reply-To: <20260304165223.2166175-1-aesteve@redhat.com> References: <20260304165223.2166175-1-aesteve@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" Add SHMEM_MAP/_UNMAP request to the vhost-user spec documentation. Reviewed-by: Stefano Garzarella Reviewed-by: Alyssa Ross Reviewed-by: Stefan Hajnoczi Reviewed-by: Manos Pitsidianakis Signed-off-by: Albert Esteve --- docs/interop/vhost-user.rst | 61 +++++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst index 4c1538cf88..08a5e43988 100644 --- a/docs/interop/vhost-user.rst +++ b/docs/interop/vhost-user.rst @@ -350,6 +350,27 @@ Device state transfer parameters In the future, additional phases might be added e.g. to allow iterative migration while the device is running. =20 +MMAP request +^^^^^^^^^^^^ + ++-------+---------+-----------+------------+-----+-------+ +| shmid | padding | fd_offset | shm_offset | len | flags | ++-------+---------+-----------+------------+-----+-------+ + +:shmid: a 8-bit shared memory region identifier + +:fd_offset: a 64-bit offset of this area from the start + of the supplied file descriptor + +:shm_offset: a 64-bit offset from the start of the + pointed shared memory region + +:len: a 64-bit size of the memory to map + +:flags: a 64-bit value: + - 0: Pages are mapped read-only + - 1: Pages are mapped read-write + C structure ----------- =20 @@ -375,6 +396,7 @@ In QEMU the vhost-user message is implemented with the = following struct: VhostUserInflight inflight; VhostUserShared object; VhostUserTransferDeviceState transfer_state; + VhostUserMMap mmap; }; } QEMU_PACKED VhostUserMsg; =20 @@ -1067,6 +1089,7 @@ Protocol features #define VHOST_USER_PROTOCOL_F_SHARED_OBJECT 18 #define VHOST_USER_PROTOCOL_F_DEVICE_STATE 19 #define VHOST_USER_PROTOCOL_F_GET_VRING_BASE_INFLIGHT 20 + #define VHOST_USER_PROTOCOL_F_SHMEM_MAP 21 =20 Front-end message types ----------------------- @@ -1888,6 +1911,44 @@ is sent by the front-end. when the operation is successful, or non-zero otherwise. Note that if the operation fails, no fd is sent to the backend. =20 +``VHOST_USER_BACKEND_SHMEM_MAP`` + :id: 9 + :equivalent ioctl: N/A + :request payload: fd and ``struct VhostUserMMap`` + :reply payload: N/A + + When the ``VHOST_USER_PROTOCOL_F_SHMEM`` protocol feature has been + successfully negotiated, this message can be submitted by the backends to + advertise a new mapping to be made in a given VIRTIO Shared Memory Regio= n. + Upon receiving the message, the front-end will mmap the given fd into the + VIRTIO Shared Memory Region with the requested ``shmid``. + If ``VHOST_USER_PROTOCOL_F_REPLY_ACK`` is negotiated, and + back-end set the ``VHOST_USER_NEED_REPLY`` flag, the front-end + must respond with zero when operation is successfully completed, + or non-zero otherwise. + + Mapping over an already existing map is not allowed and requests shall f= ail. + Therefore, the memory range in the request must correspond with a valid, + free region of the VIRTIO Shared Memory Region. Also, note that mappings + consume resources and that the request can fail when there are no resour= ces + available. Lastly, mappings are automatically unmapped by the front-end + across device reset operation. + +``VHOST_USER_BACKEND_SHMEM_UNMAP`` + :id: 10 + :equivalent ioctl: N/A + :request payload: ``struct VhostUserMMap`` + :reply payload: N/A + + When the ``VHOST_USER_PROTOCOL_F_SHMEM`` protocol feature has been + successfully negotiated, this message can be submitted by the backends so + that the front-end un-mmaps a given range (``shm_offset``, ``len``) in t= he + VIRTIO Shared Memory Region with the requested ``shmid``. Note that the + given range shall correspond to the entirety of a valid mapped region. + If ``VHOST_USER_PROTOCOL_F_REPLY_ACK`` is negotiated, and the back-end + sets the ``VHOST_USER_NEED_REPLY`` flag, the front-end must respond with + zero when operation is successfully completed, or non-zero otherwise. + .. _reply_ack: =20 VHOST_USER_PROTOCOL_F_REPLY_ACK --=20 2.52.0