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When memory is dynamically added/removed, iommu_mem_notifier() is invoked. This routine traverses through all the DMA windows (DDW only, not default windows) to add/remove "direct" TCE mappings. The routines for this purpose are tce_clearrange_multi_pSeriesLP() and tce_clearrange_multi_pSeriesLP(). Both these routines are designed for Direct mapped DMA windows only. The issue is that there could be some DMA windows in the list which are not "direct" mapped. Calling these routines will either, 1) remove some dynamically mapped TCEs, Or 2) try to add TCEs which are out of bounds and HCALL returns H_PARAMETER Here are the side affects when these routines are incorrectly invoked for "dynamically" mapped DMA windows. tce_setrange_multi_pSeriesLP() This adds direct mapped TCEs. Now, this could invoke HCALL to add TCEs with out-of-bound range. In this scenario, HCALL will return H_PARAMETER and DLAR ADD of memory will fail. tce_clearrange_multi_pSeriesLP() This will remove range of TCEs. The TCE range that is calculated, depending on the memory range being added, could infact be mapping some other memory address (for dynamic DMA window scenario). This will wipe out those TCEs. The solution is for iommu_mem_notifier() to only invoke these routines for "direct" mapped DMA windows. Signed-off-by: Gaurav Batra <gbatra@linux.vnet.ibm.com> Reviewed-by: Brian King <brking@linux.vnet.ibm.com> [mpe: Initialise direct at allocation time in ddw_list_new_entry()] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20230613171641.15641-1-gbatra@linux.vnet.ibm.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.