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

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2023/3/8 8:35, Jason Gunthorpe wrote:
> From: Nicolin Chen<nicolinc@nvidia.com>
> 
> 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@nvidia.com>
> Reviewed-by: Kevin Tian<kevin.tian@intel.com>
> Signed-off-by: Nicolin Chen<nicolinc@nvidia.com>
> Signed-off-by: Jason Gunthorpe<jgg@nvidia.com>

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>

Best regards,
baolu