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vmm: add pci_segment mmio aperture configs

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When using multiple PCI segments, the 32-bit and 64-bit mmio
aperture is split equally between each segment. Add an option
to configure the 'weight'. For example, a PCI segment with a
`mmio32_aperture_weight` of 2 will be allocated twice as much
32-bit mmio space as a normal PCI segment.

Signed-off-by: Thomas Barrett <tbarrett@crusoeenergy.com>
This commit is contained in:
Thomas Barrett
2024-04-14 19:50:45 +00:00
committed by Bo Chen
parent a84bc06874
commit e7e856d8ac
8 changed files with 334 additions and 16 deletions
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29
docs/vfio.md
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@@ -122,4 +122,31 @@ $ ls /sys/kernel/iommu_groups/22/devices/
This means these two devices are under the same IOMMU group 22. In such case,
it is important to bind both devices to VFIO and pass them both through the
VM, otherwise this could cause some functional and security issues.
VM, otherwise this could cause some functional and security issues.
### Advanced Configuration Options
Some VFIO devices have a 32-bit mmio BAR. When using many such devices, it is
possible to exhaust the 32-bit mmio space available on a PCI segment. The
following example demonstrates an example device with a 16 MiB 32-bit mmio BAR.
```
lspci -s 0000:01:00.0 -v
0000:01:00.0 3D controller: NVIDIA Corporation Device 26b9 (rev a1)
[...]
Memory at f9000000 (32-bit, non-prefetchable) [size=16M]
Memory at 46000000000 (64-bit, prefetchable) [size=64G]
Memory at 48040000000 (64-bit, prefetchable) [size=32M]
[...]
```
When using multiple PCI segments, the 32-bit mmio address space available to
be allocated to VFIO devices is equally split between all PCI segments by
default. This can be tuned with the `--pci-segment` flag. The following example
demonstrates a guest with two PCI segments. 2/3 of the 32-bit mmio address
space is available for use by devices on PCI segment 0 and 1/3 of the 32-bit
mmio address space is available for use by devices on PCI segment 1.
```
--platform num_pci_segments=2
--pci-segment pci_segment=0,mmio32_aperture_weight=2
--pci-segment pci_segment=1,mmio32_aperture_weight=1
```