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docs: Add hotplug behind IOMMU segment to documentation

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Signed-off-by: Rob Bradford <robert.bradford@intel.com>
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Rob Bradford 2022-03-22 10:40:03 +00:00
parent 1756b23aea
commit 3120260ed6
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docs/iommu.md
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@ -231,3 +231,38 @@ Last thing is to start the L2 guest with the huge pages memory backend.
--cmdline "console=ttyS0 console=hvc0 root=/dev/vda1 rw" \
--device path=/sys/bus/pci/devices/0000:00:04.0
```
### Dedicated IOMMU PCI segments
To facilitate hotplug of devices that require being behind an IOMMU it is
possible to mark entire PCI segments as behind the IOMMU.
This is accomplished through `--platform
num_pci_segments=<number_of_segments>,iommu_segments=<range of segments>` or
via the equivalents in `PlatformConfig` for the API.
e.g.
```bash
./cloud-hypervisor \
--api-socket=/tmp/api \
--cpus boot=1 \
--memory size=4G,hugepages=on \
--disk path=focal-server-cloudimg-amd64.raw \
--kernel custom-vmlinux \
--cmdline "console=ttyS0 console=hvc0 root=/dev/vda1 rw" \
--platform num_pci_segments=2,iommu_segments=1
```
This adds a second PCI segment to the platform behind the IOMMU. A VFIO device
requiring the IOMMU then may be hotplugged:
e.g.
```bash
./ch-remote --api-socket=/tmp/api add-device path=/sys/bus/pci/devices/0000:00:04.0,iommu=on,pci_segment=1
```
Devices that cannot be placed behind an IOMMU (e.g. lacking an `iommu=` option)
cannot be placed on the IOMMU segments.