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Prior to commit092edaddb6("iommu: Support mm PASID 1:n with sva domains") the code allowed a SVA handle to be bound multiple times to the same (mm, device) pair. This was alluded to in the kdoc comment, but we had understood this to be more a remark about allowing multiple devices, not a literal same-driver re-opening the same SVA. It turns out uacce and idxd were both relying on the core code to handle reference counting for same-device same-mm scenarios. As this looks hard to resolve in the drivers bring it back to the core code. The new design has changed the meaning of the domain->users refcount to refer to the number of devices that are sharing that domain for the same mm. This is part of the design to lift the SVA domain de-duplication out of the drivers. Return the old behavior by explicitly de-duplicating the struct iommu_sva handle. The same (mm, device) will return the same handle pointer and the core code will handle tracking this. The last unbind of the handle will destroy it. Fixes:092edaddb6("iommu: Support mm PASID 1:n with sva domains") Reported-by: Zhangfei Gao <zhangfei.gao@linaro.org> Closes: https://lore.kernel.org/all/20240221110658.529-1-zhangfei.gao@linaro.org/ Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com> Link: https://lore.kernel.org/r/0-v1-9455fc497a6f+3b4-iommu_sva_sharing_jgg@nvidia.com Signed-off-by: Joerg Roedel <jroedel@suse.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.