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a26f2e4e68
Some device specific IOMMU parent drivers have long standing bogus behaviour that mistakenly clean up the maps during .reset. By definition, this is violation to the on-chip IOMMU ops (i.e. .set_map, or .dma_map & .dma_unmap) in those offending drivers, as the removal of internal maps is completely agnostic to the upper layer, causing inconsistent view between the userspace and the kernel. Some userspace app like QEMU gets around of this brokenness by proactively removing and adding back all the maps around vdpa device reset, but such workaround actually penaltize other well-behaved driver setup, where vdpa reset always comes with the associated mapping cost, especially for kernel vDPA devices (use_va=false) that have high cost on pinning. It's imperative to rectify this behaviour and remove the problematic code from all those non-compliant parent drivers. However, we cannot unconditionally remove the bogus map-cleaning code from the buggy .reset implementation, as there might exist userspace apps that already rely on the behaviour on some setup. Introduce a .compat_reset driver op to keep compatibility with older userspace. New and well behaved parent driver should not bother to implement such op, but only those drivers that are doing or used to do non-compliant map-cleaning reset will have to. Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com> Message-Id: <1697880319-4937-5-git-send-email-si-wei.liu@oracle.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Tested-by: Lei Yang <leiyang@redhat.com>
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.