Gunyah is an open-source Type-1 hypervisor developed by Qualcomm. It does not depend on any lower-privileged OS/kernel code for its core functionality. This increases its security and can support a smaller trusted computing based when compared to Type-2 hypervisors. Add documentation describing the Gunyah hypervisor and the main components of the Gunyah hypervisor which are of interest to Linux virtualization development. Signed-off-by: Elliot Berman <quic_eberman@xxxxxxxxxxx> --- Documentation/virt/gunyah/index.rst | 135 ++++++++++++++++++++++++++++ Documentation/virt/gunyah/message-queue.rst | 68 ++++++++++++++ Documentation/virt/index.rst | 1 + 3 files changed, 204 insertions(+) diff --git a/Documentation/virt/gunyah/index.rst b/Documentation/virt/gunyah/index.rst new file mode 100644 index 0000000000000..fba2c7a11d0f8 --- /dev/null +++ b/Documentation/virt/gunyah/index.rst @@ -0,0 +1,135 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================= +Gunyah Hypervisor +================= + +.. toctree:: + :maxdepth: 1 + + message-queue + +Gunyah is a Type-1 hypervisor which is independent of any OS kernel, and runs in +a more privileged CPU level (EL2 on Aarch64). It does not depend on a less +privileged operating system for its core functionality. This increases its +security and can support a much smaller trusted computing base than a Type-2 +hypervisor. + +Gunyah is an open source hypervisor. The source repository is available at +https://github.com/quic/gunyah-hypervisor. + +Gunyah provides these following features. + +- Scheduling: + + A scheduler for virtual CPUs (vCPUs) on physical CPUs enables time-sharing + of the CPUs. Gunyah supports two models of scheduling which can coexist on + a running system: + + 1. Hypervisor vCPU scheduling in which Gunyah hypervisor schedules vCPUS on + its own. The default is a real-time priority with round-robin scheduler. + 2. "Proxy" scheduling in which an owner-VM can donate the remainder of its + own vCPU's time slice to an owned-VM's vCPU via a hypercall. + +- Memory Management: + + APIs handling memory, abstracted as objects, limiting direct use of physical + addresses. Memory ownership and usage tracking of all memory under its control. + Memory partitioning between VMs is a fundamental security feature. + +- Interrupt Virtualization: + + Interrupt ownership is tracked and interrupt delivery is directly to the + assigned VM. Gunyah makes use of hardware interrupt virtualization where + possible. + +- Inter-VM Communication: + + There are several different mechanisms provided for communicating between VMs. + + 1. Message queues + 2. Doorbells + 3. Virtio MMIO transport + 4. Shared memory + +- Virtual platform: + + Architectural devices such as interrupt controllers and CPU timers are + directly provided by the hypervisor as well as core virtual platform devices + and system APIs such as ARM PSCI. + +- Device Virtualization: + + Para-virtualization of devices is supported using inter-VM communication and + virtio transport support. Select stage 2 faults by virtual machines that use + proxy-scheduled vCPUs can be handled directly by Linux to provide Type-2 + hypervisor style on-demand paging and/or device emulation. + +Architectures supported +======================= +AArch64 with a GICv3 or GICv4.1 + +Resources and Capabilities +========================== + +Services/resources provided by the Gunyah hypervisor are accessible to a +virtual machine through capabilities. A capability is an access control +token granting the holder a set of permissions to operate on a specific +hypervisor object (conceptually similar to a file-descriptor). +For example, inter-VM communication using Gunyah doorbells and message queues +is performed using hypercalls taking Capability ID arguments for the required +IPC objects. These resources are described in Linux as a struct gunyah_resource. + +Unlike UNIX file descriptors, there is no path-based or similar lookup of +an object to create a new Capability, meaning simpler security analysis. +Creation of a new Capability requires the holding of a set of privileged +Capabilities which are typically never given out by the Resource Manager (RM). + +Gunyah itself provides no APIs for Capability ID discovery. Enumeration of +Capability IDs is provided by RM as a higher level service to VMs. + +Resource Manager +================ + +The Gunyah Resource Manager (RM) is a privileged application VM supporting the +Gunyah Hypervisor. It provides policy enforcement aspects of the virtualization +system. The resource manager can be treated as an extension of the Hypervisor +but is separated to its own partition to ensure that the hypervisor layer itself +remains small and secure and to maintain a separation of policy and mechanism in +the platform. The resource manager runs at arm64 NS-EL1, similar to other +virtual machines. + +Communication with the resource manager from other virtual machines happens as +described in message-queue.rst. Details about the specific messages can be found +in drivers/virt/gunyah/rsc_mgr.c + +:: + + +-------+ +--------+ +--------+ + | RM | | VM_A | | VM_B | + +-.-.-.-+ +---.----+ +---.----+ + | | | | + +-.-.-----------.------------.----+ + | | \==========/ | | + | \========================/ | + | Gunyah | + +---------------------------------+ + +The source for the resource manager is available at +https://github.com/quic/gunyah-resource-manager. + +The resource manager provides the following features: + +- VM lifecycle management: allocating a VM, starting VMs, destruction of VMs +- VM access control policy, including memory sharing and lending +- Interrupt routing configuration +- Forwarding of system-level events (e.g. VM shutdown) to owner VM +- Resource (capability) discovery + +A VM requires boot configuration to establish communication with the resource +manager. This is provided to VMs via a 'hypervisor' device tree node which is +overlaid to the VMs DT by the RM. This node lets guests know they are running +as a Gunyah guest VM, how to communicate with resource manager, and basic +description and capabilities of this VM. See +Documentation/devicetree/bindings/firmware/gunyah-hypervisor.yaml for a +description of this node. diff --git a/Documentation/virt/gunyah/message-queue.rst b/Documentation/virt/gunyah/message-queue.rst new file mode 100644 index 0000000000000..96864708f442e --- /dev/null +++ b/Documentation/virt/gunyah/message-queue.rst @@ -0,0 +1,68 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Message Queues +============== +Message queue is a simple low-capacity IPC channel between two virtual machines. +It is intended for sending small control and configuration messages. Each +message queue is unidirectional and buffered in the hypervisor. A full-duplex +IPC channel requires a pair of queues. + +The size of the queue and the maximum size of the message that can be passed is +fixed at creation of the message queue. Resource manager is presently the only +use case for message queues, and creates messages queues between itself and VMs +with a fixed maximum message size of 240 bytes. Longer messages require a +further protocol on top of the message queue messages themselves. For instance, +communication with the resource manager adds a header field for sending longer +messages which are split into smaller fragments. + +The diagram below shows how message queue works. A typical configuration +involves 2 message queues. Message queue 1 allows VM_A to send messages to VM_B. +Message queue 2 allows VM_B to send messages to VM_A. + +1. VM_A sends a message of up to 240 bytes in length. It makes a hypercall + with the message to request the hypervisor to add the message to + message queue 1's queue. The hypervisor copies memory into the internal + message queue buffer; the memory doesn't need to be shared between + VM_A and VM_B. + +2. Gunyah raises the corresponding interrupt for VM_B (Rx vIRQ) when any of + these happens: + + a. gunyah_msgq_send() has PUSH flag. This is a typical case when the message + queue is being used to implement an RPC-like interface. + b. Explicitly with gunyah_msgq_push hypercall from VM_A. + c. Message queue has reached a threshold depth. Typically, this threshold + depth is the size of the queue (in other words: when queue is full, Rx + vIRQ is raised). + +3. VM_B calls gunyah_msgq_recv() and Gunyah copies message to requested buffer. + +4. Gunyah raises the corresponding interrupt for VM_A (Tx vIRQ) when the message + queue falls below a watermark depth. Typically, this is when the queue is + drained. Note the watermark depth and the threshold depth for the Rx vIRQ are + independent values. Coincidentally, this signal is conceptually similar to + Clear-to-Send. + +For VM_B to send a message to VM_A, the process is identical, except that +hypercalls reference message queue 2's capability ID. The IRQ will be different +for the second message queue. + +:: + + +-------------------+ +-----------------+ +-------------------+ + | VM_A | |Gunyah hypervisor| | VM_B | + | | | | | | + | | | | | | + | | Tx | | | | + | |-------->| | Rx vIRQ | | + |gunyah_msgq_send() | Tx vIRQ |Message queue 1 |-------->|gunyah_msgq_recv() | + | |<------- | | | | + | | | | | | + | | | | | | + | | | | Tx | | + | | Rx vIRQ | |<--------| | + |gunyah_msgq_recv() |<--------|Message queue 2 | Tx vIRQ |gunyah_msgq_send() | + | | | |-------->| | + | | | | | | + | | | | | | + +-------------------+ +-----------------+ +---------------+ diff --git a/Documentation/virt/index.rst b/Documentation/virt/index.rst index 7fb55ae08598d..15869ee059b35 100644 --- a/Documentation/virt/index.rst +++ b/Documentation/virt/index.rst @@ -16,6 +16,7 @@ Virtualization Support coco/sev-guest coco/tdx-guest hyperv/index + gunyah/index .. only:: html and subproject -- 2.34.1
