From b3dc643ffb494a52a01883f5caec515bf9626c38 Mon Sep 17 00:00:00 2001 From: Thomas Lamprecht Date: Fri, 18 Nov 2022 11:16:03 +0100 Subject: [PATCH] pci passthrough: rework IOMMU sections a bit Signed-off-by: Thomas Lamprecht --- qm-pci-passthrough.adoc | 31 +++++++++++++++---------------- 1 file changed, 15 insertions(+), 16 deletions(-) diff --git a/qm-pci-passthrough.adoc b/qm-pci-passthrough.adoc index 10f3cf4..df6cf21 100644 --- a/qm-pci-passthrough.adoc +++ b/qm-pci-passthrough.adoc @@ -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