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Currently scratch PTEs are write-enabled and points to a single scratch page. This has the side effect that buggy applications with out-of-bounds memory accesses may not notice the bad access since what's written may be read back. Instead use NULL PTEs as scratch PTEs. These always return 0 when reading, and writing has no effect. As a slight benefit, we can also use huge NULL PTEs. One drawback pointed out is that debugging may be hampered since previously when inspecting the content of the scratch page, it might be possible to detect writes to out-of-bound addresses and possibly also from where the out-of-bounds address originated. However since the scratch page-table structure is kept, it will be easy to add back the single RW-enabled scratch page under a debug define if needed. Also update the kerneldoc accordingly and move the function to create the scratch page-tables from xe_pt.c to xe_pt.h since it is accessing vm structure internals and this also makes it possible to make it static. v2: - Don't try to encode scratch PTEs larger than 1GiB. - Move xe_pt_create_scratch(), Update kerneldoc. v3: - Rebase. Cc: Brian Welty <brian.welty@intel.com> Cc: Matt Roper <matthew.d.roper@intel.com> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com> Acked-by: Lucas De Marchi <lucas.demarchi@intel.com> #for general direction. Reviewed-by: Brian Welty <brian.welty@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20231209151843.7903-3-thomas.hellstrom@linux.intel.com Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.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.