[pve-devel] [PATCH docs 2/2] pcie-passthrough: add short note about iommu passthrough mode

Dominik Csapak d.csapak at proxmox.com
Fri May 20 10:43:25 CEST 2022

that explains in one sentence what it does, that it can increase
performance and how to activate it.

Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
 qm-pci-passthrough.adoc | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/qm-pci-passthrough.adoc b/qm-pci-passthrough.adoc
index 5ef325d..28bb4fc 100644
--- a/qm-pci-passthrough.adoc
+++ b/qm-pci-passthrough.adoc
@@ -62,6 +62,24 @@ The command line parameters are:
 * 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=1
+ iommu=pt
+to the kernel commandline.
 .Kernel Modules
 You have to make sure the following modules are loaded. This can be achieved by

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