On 11/18/20 9:52 PM, Will Deacon wrote:
On Fri, Sep 25, 2020 at 12:06:17PM -0700, Ashok Raj wrote:
Presently, the default domain of an iommu group is allocated during boot time
and it cannot be changed later. So, the device would typically be either in
identity (pass_through) mode or the device would be in DMA mode as long as the
system is up and running. There is no way to change the default domain type
dynamically i.e. after booting, a device cannot switch between identity mode and
DMA mode.
Assume a use case wherein the privileged user would want to use the device in
pass-through mode when the device is used for host so that it would be high
performing. Presently, this is not supported. Hence add support to change the
default domain of an iommu group dynamically.
Support this by writing to a sysfs file, namely
"/sys/kernel/iommu_groups/<grp_id>/type".
Testing:
--------
Tested by dynamically changing storage device (nvme) from
1. identity mode to DMA and making sure file transfer works
2. DMA mode to identity mode and making sure file transfer works
Tested only for intel_iommu/vt-d. Would appreciate if someone could test on AMD
and ARM based machines.
Based on iommu maintainer's 'next' branch.
Modulo my minor comments, I think this looks good for 5.11 if you can
please send a version 9.
Robin -- please can you give it the once-over too? I think root can break
things quite badly with this interface, but root can do that in other ways
anyway...
Sure. I will send a v9 after Robin's review.
Will
Best regards,
baolu
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