Re: [PATCH v2 11/17] iommu: Introduce a new iommu_group_replace_domain() API

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On 2023/3/8 8:35, Jason Gunthorpe wrote:
From: Nicolin Chen<nicolinc@xxxxxxxxxx>

qemu has a need to replace the translations associated with a domain
when the guest does large-scale operations like switching between an
IDENTITY domain and, say, dma-iommu.c.

Currently, it does this by replacing all the mappings in a single
domain, but this is very inefficient and means that domains have to be
per-device rather than per-translation.

Provide a high-level API to allow replacements of one domain with
another. This is similar to a detach/attach cycle except it doesn't
force the group to go to the blocking domain in-between.

By removing this forced blocking domain the iommu driver has the
opportunity to implement a non-disruptive replacement of the domain to the
greatest extent its hardware allows. This allows the qemu emulation of the
vIOMMU to be more complete, as real hardware often has a non-distruptive
replacement capability.

It could be possible to address this by simply removing the protection
from the iommu_attach_group(), but it is not so clear if that is safe for
the few users. Thus, add a new API to serve this new purpose.

All drivers are already required to support changing between active
UNMANAGED domains when using their attach_dev ops.

This API is expected to be used only by IOMMUFD, so add to the iommu-priv
header and mark it as IOMMUFD_INTERNAL.

Suggested-by: Jason Gunthorpe<jgg@xxxxxxxxxx>
Reviewed-by: Kevin Tian<kevin.tian@xxxxxxxxx>
Signed-off-by: Nicolin Chen<nicolinc@xxxxxxxxxx>
Signed-off-by: Jason Gunthorpe<jgg@xxxxxxxxxx>

Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>

Best regards,
baolu



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