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pci passthrough: rework IOMMU sections a bit

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Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
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Thomas Lamprecht 2022-11-18 11:16:03 +01:00
parent e6820561d4
commit b3dc643ffb
1 changed files with 15 additions and 16 deletions
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qm-pci-passthrough.adoc
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@ -44,34 +44,33 @@ some configuration to enable PCI(e) passthrough.
.IOMMU
First, the IOMMU support has to be enabled in your BIOS/UEFI. Most often, that
options is named `IOMMU` or `VT-d`, but check the manual for your motherboard
for the exact option you need to enable.
First, you have to enable IOMMU support in your BIOS/UEFI. Usually the
corresponding setting is called `IOMMU` or `VT-d`,but you should find the exact
option name in the manual of your motherboard.
Then, the IOMMU might need to be activated on the
xref:sysboot_edit_kernel_cmdline[kernel commandline].
(On newer kernels, this should not be necessary.)
For Intel CPUs, you may also need to enable the IOMMU on the
xref:sysboot_edit_kernel_cmdline[kernel command line] for older (pre-5.15)
kernels by adding:
The command line parameters are:
* for Intel CPUs:
+
----
intel_iommu=on
----
* for AMD CPUs it should be enabled automatically.
For AMD CPUs it should be enabled automatically.
If your hardware supports it, enabling IOMMU passthrough mode might increase
performance, because then the VMs bypass the (default) DMA translation
which is normally done by the hypervisor, before handing DMA requests off to
the hardware IOMMU. You can enable it with adding
.IOMMU Passthrough Mode
If your hardware supports IOMMU passthrough mode, enabling this mode might
increase performance.
This is because VMs then bypass the (default) DMA translation normally
performed by the hyper-visor and instead pass DMA requests directly to the
hardware IOMMU. To enable these options, add:
----
iommu=pt
----
to the kernel commandline.
to the xref:sysboot_edit_kernel_cmdline[kernel commandline].
.Kernel Modules