Fork of alistair23 Linux kernel for reMarkable from https://github.com/alistair23/linux
6e301a8e56
The powernv platform maintains 2 TCE tables for VFIO - a hardware TCE table and a table with userspace addresses. These tables are radix trees, we allocate indirect levels when they are written to. Since the memory allocation is problematic in real mode, we have 2 accessors to the entries: - for virtual mode: it allocates the memory and it is always expected to return non-NULL; - fr real mode: it does not allocate and can return NULL. Also, DMA windows can span to up to 55 bits of the address space and since we never have this much RAM, such windows are sparse. However currently the SPAPR TCE IOMMU driver walks through all TCEs to unpin DMA memory. Since we maintain a userspace addresses table for VFIO which is a mirror of the hardware table, we can use it to know which parts of the DMA window have not been mapped and skip these so does this patch. The bare metal systems do not have this problem as they use a bypass mode of a PHB which maps RAM directly. This helps a lot with sparse DMA windows, reducing the shutdown time from about 3 minutes per 1 billion TCEs to a few seconds for 32GB sparse guest. Just skipping the last level seems to be good enough. As non-allocating accessor is used now in virtual mode as well, rename it from IOMMU_TABLE_USERSPACE_ENTRY_RM (real mode) to _RO (read only). Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru> Signed-off-by: Paul Mackerras <paulus@ozlabs.org> |
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README
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.