41 lines
1.7 KiB
ReStructuredText
41 lines
1.7 KiB
ReStructuredText
.. _mmio-device-passthrough:
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MMIO Device Passthrough
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########################
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The ACRN Hypervisor supports both PCI and MMIO device passthrough.
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However there are some constraints on and hypervisor assumptions about
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MMIO devices: there can be no DMA access to the MMIO device and the MMIO
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device may not use IRQs.
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Here is how ACRN supports MMIO device passthrough:
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* For a pre-launched VM, the VM configuration tells the ACRN hypervisor
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the addresses of the physical MMIO device's regions and where they are
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mapped to in the pre-launched VM. The hypervisor then removes these
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MMIO regions from the Service VM and fills the vACPI table for this MMIO
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device based on the device's physical ACPI table.
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* For a post-launched VM, the same actions are done as in a
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pre-launched VM, plus we use the command line to tell which MMIO
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device we want to pass through to the post-launched VM.
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If the MMIO device has ACPI Tables, use ``--acpidev_pt HID`` and
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if not, use ``--mmiodev_pt MMIO_regions``.
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.. note::
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Currently, the vTPM and PT TPM in the ACRN-DM have the same HID so we
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can't support them both at the same time. The VM will fail to boot if
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both are used.
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These issues remain to be implemented:
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* Save the MMIO regions in a field of the VM structure in order to
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release the resources when the post-launched VM shuts down abnormally.
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* Allocate the guest MMIO regions for the MMIO device in a guest-reserved
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MMIO region instead of being hard-coded. With this, we could add more
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passthrough MMIO devices.
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* De-assign the MMIO device from the Service VM first before passing
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through it to the post-launched VM and not only removing the MMIO
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regions from the Service VM.
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