What is the IOMMU configuration used for the Intel machines?

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                          In kernel boot options (https://www.kernel.org/doc/Documentation/x86/x86_64/boot-options.txt)  I noticed the following option:

     iommu=[][,noagp][,off][,force][,noforce]
    	[,memaper[=]][,merge][,fullflush][,nomerge]
    	[,noaperture][,calgary]
    
      General iommu options:
        off                Don't initialize and use any kind of IOMMU.
        noforce            Don't force hardware IOMMU usage when it is not needed.
                           (default).
        force              Force the use of the hardware IOMMU even when it is
                           not actually needed (e.g. because < 3 GB memory).
        soft               Use software bounce buffering (SWIOTLB) (default for
                           Intel machines). This can be used to prevent the usage
                           of an available hardware IOMMU.

It mentions that iommu=soft is the default option for Intel machines and also mentions that it can be used to prevent the use of a hardware IOMMU. 

So if this option is the default for Intel machines, do Intel machines not use hardware IOMMU or do they use hardware IOMMU + software bounce buffering by default?  

Also, is there a way to see which IOMMU configuration is being used in the kernel after bootup? 
                        

Asked by sammy17 (115 rep)

Jun 2, 2023, 08:05 PM
Last activity: Jun 4, 2023, 08:58 AM

What is the IOMMU configuration used for the Intel machines?

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