Messages in this thread | | | Subject | Re: [RFC PATCH 0/4] iommu: Per-group default domain type | From | Lu Baolu <> | Date | Wed, 22 Jan 2020 12:58:42 +0800 |
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Hi,
On 1/21/20 6:14 PM, John Garry wrote: > On 21/01/2020 00:43, Lu Baolu wrote: >>>> An IOMMU group represents the smallest set of devices that are >>>> considered >>>> to be isolated. All devices belonging to an IOMMU group share a default >>>> domain for DMA APIs. There are two types of default domain: >>>> IOMMU_DOMAIN_DMA >>>> and IOMMU_DOMAIN_IDENTITY. The former means IOMMU translation, while >>>> the >>>> latter means IOMMU by-pass. >>>> >>>> Currently, the default domain type for the IOMMU groups is determined >>>> globally. All IOMMU groups use a single default domain type. The global >>>> default domain type can be adjusted by kernel build configuration or >>>> kernel parameters. >>>> >>>> More and more users are looking forward to a fine grained default >>>> domain >>>> type. For example, with the global default domain type set to >>>> translation, >>>> the OEM verndors or end users might want some trusted and fast-speed >>>> devices >>>> to bypass IOMMU for performance gains. On the other hand, with global >>>> default domain type set to by-pass, some devices with limited system >>>> memory addressing capability might want IOMMU translation to remove the >>>> bounce buffer overhead. >>> >>> Hi Lu Baolu, >>> >>> Do you think that it would be a more common usecase to want >>> kernel-managed devices to be passthrough for performance reasons and >>> some select devices to be in DMA domain, like those with limited >>> address cap or whose drivers request huge amounts of memory? >>> >>> I just think it would be more manageable to set kernel commandline >>> parameters for this, i.e. those select few which want DMA domain. >>> > > Hi Baolu, > >> >> It's just two sides of a coin. Currently, iommu subsystem make DMA >> domain by default, that's the reason why I selected to let user set >> which devices are willing to use identity domains. >> > > OK, understood. > > There was an alternate solution here which would allow per-group type to > be updated via sysfs: > > https://lore.kernel.org/linux-iommu/cover.1566353521.git.sai.praneeth.prakhya@intel.com/ >
Yes. My patch set just tries to do this statically during boot time.
> > Any idea what happened to that?
No idea. Sai might have more information. :-)
Best regards, baolu
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