virt/hyperv/vmbus.rst

5 VMBus is a software construct provided by Hyper-V to guest VMs.  It
7 devices that Hyper-V presents to guest VMs.   The control path is
8 used to offer synthetic devices to the guest VM and, in some cases,
10 channels for communicating between the device driver in the guest VM
12 signaling primitives to allow Hyper-V and the guest to interrupt
16 entry in a running Linux guest.  The VMBus driver (drivers/hv/vmbus_drv.c)
37 Guest VMs may have multiple instances of the synthetic SCSI
47 the device in the guest VM.  For example, the Linux driver for the
65 guest, and the "out" ring buffer is for messages from the guest to
67 viewed by the guest side.  The ring buffers are memory that is
68 shared between the guest and the host, and they follow the standard
69 paradigm where the memory is allocated by the guest, with the list
74 guest and is specific to each synthetic device.   The list of GPAs
98 Hyper-V enforces a limit on the aggregate amount of guest memory
100 that a rogue guest can't force the consumption of excessive host
116 * Request/response:  One side (usually the guest) sends a message
121 flight simultaneously, so the guest specifies a transactionID when
128 between the guest and the Hyper-V host, the actual data to be
134 Hyper-V host to the guest contain the actual time value.  When the
147    of guest memory can be targeted.
151    single logical area of guest memory to be targeted.
156 technologies that fully encrypt guest memory and that allow the
157 guest to not trust the hypervisor (AMD SEV-SNP, Intel TDX), trusting
162 messages read by the guest from the "in" ring buffer are copied to a
170 Hyper-V provides each guest CPU with a synthetic interrupt controller
171 that is used by VMBus for host-guest communication. While each synic
174 the Hyper-V host and a guest CPU use that SINT.
178 each CPU in the guest has a synic and may receive VMBus interrupts,
201 VMBus provides a mechanism for the guest to interrupt the host when
202 the guest has queued new messages in a ring buffer.  The host
203 expects that the guest will send an interrupt only when an "out"
204 ring buffer transitions from empty to non-empty.  If the guest sends
206 unnecessary.  If a guest sends an excessive number of unnecessary
207 interrupts, the host may throttle that guest by suspending its
210 Similarly, the host will interrupt the guest via the synic when
223 The guest CPU that a VMBus channel will interrupt is selected by the
224 guest when the channel is created, and the host is informed of that
252 An online CPU in a Linux guest may not be taken offline if it has
263 channel is being changed via sysfs, the guest doesn't know exactly
270 Hyper-V and the Linux guest have a separate message-passing path
275 The first step is for the guest to connect to the generic
277 the guest and Hyper-V agree on a VMBus protocol version they will
281 The guest then tells Hyper-V to "send offers".  Hyper-V sends an
282 offer message to the guest for each synthetic device that the VM
296 Upon receipt of an offer message, the guest identifies the device
302 the corresponding VSP. It allocates guest memory for the channel
318 The Hyper-V host can send a "rescind" message to the guest to