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doc: edit ivshmem hld doc
Signed-off-by: David B. Kinder <david.b.kinder@intel.com>
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David B. Kinder
David Kinder
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@ -3,10 +3,10 @@
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ACRN Shared Memory Based Inter-VM Communication
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###############################################
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To support inter virtual machines communication based on shared memory
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mechanism, ACRN device model/hypervisor emulate a virtual PCI device
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(Called ``ivshmem`` device) to expose the base address and size of shared
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memory.
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ACRN supports inter-virtual machine communication based on a shared
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memory mechanism, The ACRN device model and hypervisor emulate a virtual
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PCI device (called an ``ivshmem`` device) to expose the base address and
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size of this shared memory.
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Inter-VM Communication Overview
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*******************************
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@ -17,28 +17,33 @@ Inter-VM Communication Overview
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ACRN shared memory based inter-vm communication architecture
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Two solutions of ivshmem device: dm-land and hypervisor-land. For dm-land,
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the ivshmem device emulated in acrn device model and its shared memory region
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is allocated from the Service VM's memory space. For hypervisor-land, it is
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emulated in hypervisor and the shared memory regions are reserved in hypervisor's
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memory space. The former solution only supports interactive between post-launched
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VMs and the latter one can work for both pre-launched and post-launched VMs. The
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hypervisor-land solution is WIP, plan to support in the near future.
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The ``ivshmem`` device is emulated in the ACRN device model (dm-land)
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and its shared memory region is allocated from the Service VM's memory
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space. This solution only supports communication between post-launched
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VMs.
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- Ivshmem dm – The ivshmem device model implements register virtualization
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.. note:: In a future implementation, the ``ivshmem`` device could
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instead be emulated in the hypervisor (hypervisor-land) and the shared
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memory regions reserved in the hypervisor's memory space. This solution
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would work for both pre-launched and post-launched VMs.
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ivshmem dm:
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The ivshmem device model implements register virtualization
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and shared memory mapping. Will support notification/interrupt mechanism
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in future.
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- Ivshmem server – A daemon for inter-VM notification capability,
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currently, it has not been implemented, so the inter-VM communication
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doesn’t support notification mechanism.
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ivshmem server:
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A daemon for inter-VM notification capability,
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This is currently not implemented, so the inter-VM communication
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doesn't support a notification mechanism.
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Ivshmem Device Introduction
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***************************
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The ivshmem device is a virtual standard PCI device, it consists of two
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BARs(BAR0 and BAR2), one is used for emulate interrupt related registers,
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another one is used for exposing shared memory region. The ivshmem device
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The ``ivshmem`` device is a virtual standard PCI device consisting of
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two Base Address Registers (BARs): BAR0 is used for emulating interrupt related registers,
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and BAR2 is used for exposing shared memory region. The ``ivshmem`` device
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doesn't support any extra capabilities.
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Configuration Space Definition
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@ -58,36 +63,51 @@ Configuration Space Definition
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MMIO Registers Definition
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+---------------------------+----------+-------+-----------------------------------------------------------------------------------------------------------------------+
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| Register | Offset | RW | Description |
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+===========================+==========+=======+=======================================================================================================================+
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| IVSHMEM\_IRQ\_MASK\_REG | 0x0 | R/W | Interrupt Status register is used for legacy interrupt. |
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| | | | |
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| | | | Currently, the ivshmem doesn’t support interrupt, so this is reserved. |
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+---------------------------+----------+-------+-----------------------------------------------------------------------------------------------------------------------+
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| IVSHMEM\_IRQ\_STA\_REG | 0x4 | R/W | Interrupt Mask register is used for legacy interrupt. |
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| | | | |
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| | | | Currently, the ivshmem doesn’t support interrupt, so this is reserved. |
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+---------------------------+----------+-------+-----------------------------------------------------------------------------------------------------------------------+
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| IVSHMEM\_IV\_POS\_REG | 0x8 | RO | Inter VM Position register is used to identify VM ID, currently its value is zero. |
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+---------------------------+----------+-------+-----------------------------------------------------------------------------------------------------------------------+
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| IVSHMEM\_DOORBELL\_REG | 0xc | WO | Doorbell register is used to trigger an interrupt to the peer VM. Currently, the ivshmem doesn’t support interrupt. |
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+---------------------------+----------+-------+-----------------------------------------------------------------------------------------------------------------------+
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.. list-table::
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:widths: auto
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:header-rows: 1
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* - Register
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- Offset
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- Read/Write
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- Description
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* - IVSHMEM\_IRQ\_MASK\_REG
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- 0x0
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- R/W
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- Interrupt Status register is used for legacy interrupt.
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ivshmem doesn't support interrupts, so this is reserved.
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* - IVSHMEM\_IRQ\_STA\_REG
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- 0x4
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- R/W
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- Interrupt Mask register is used for legacy interrupt.
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ivshmem doesn't support interrupts, so this is reserved.
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* - IVSHMEM\_IV\_POS\_REG
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- 0x8
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- RO
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- Inter-VM Position register is used to identify the VM ID.
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Currently its value is zero.
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* - IVSHMEM\_DOORBELL\_REG
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- 0xC
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- WO
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- Doorbell register is used to trigger an interrupt to the peer VM.
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ivshmem doesn't support interrupts.
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Usage
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*****
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To support two post-launched VMs communication via ivshmem device, user
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needs to add below line as acrn-dm boot parameter.
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To support two post-launched VMs communicating via an ``ivshmem`` device,
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add this line as an acrn-dm boot parameter::
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***-s slot, ivshmem, shm\_name,shm\_size***
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-s slot, ivshmem, shm_name, shm_size
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- -s slot – Specify the virtual PCI slot number
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where
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- ivshmem – Virtual PCI device name
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- ``-s slot`` - Specify the virtual PCI slot number
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- shm\_name – Specify a shared memory name, post-launched VMs with the
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same *shm\_name* share a shared memory region.
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- ``ivshmem`` - Virtual PCI device name
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- shm\_size – Specify a shared memory size, two communicating VMs need
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to define the same size.
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- ``shm_name`` - Specify a shared memory name. Post-launched VMs with the
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same ``shm_name`` share a shared memory region.
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- ``shm_size`` - Specify a shared memory size. The two communicating
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VMs must define the same size.
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