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iommu_mem_notifier() is invoked when RAM is dynamically added/removed. This notifier call is responsible to add/remove TCEs from the Dynamic DMA Window (DDW) when TCEs are pre-mapped. TCEs are pre-mapped only for RAM and not for persistent memory (pmemory). For DMA buffers in pmemory, TCEs are dynamically mapped when the device driver instructs to do so. The issue is 'daxctl' command is capable of adding pmemory as "System RAM" after LPAR boot. The command to do so is - daxctl reconfigure-device --mode=system-ram dax0.0 --force This will dynamically add pmemory range to LPAR RAM eventually invoking iommu_mem_notifier(). The address range of pmemory is way beyond the Max RAM that the LPAR can have. Which means, this range is beyond the DDW created for the device, at device initialization time. As a result when TCEs are pre-mapped for the pmemory range, by iommu_mem_notifier(), PHYP HCALL returns H_PARAMETER. This failed the command, daxctl, to add pmemory as RAM. The solution is to not pre-map TCEs for pmemory. Signed-off-by: Gaurav Batra <gbatra@linux.ibm.com> Tested-by: Donet Tom <donettom@linux.ibm.com> Reviewed-by: Donet Tom <donettom@linux.ibm.com> Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com> Link: https://patch.msgid.link/20250130183854.92258-1-gbatra@linux.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 reStructuredText 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.