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The placement and size of the vmemmap region in the kernel virtual address space is currently derived from the base2 order of the size of a struct page. This makes for nicely aligned constants with lots of leading 0xf and trailing 0x0 digits, but given that the actual struct pages are indexed as an ordinary array, this resulting region is severely overdimensioned when the size of a struct page is just over a power of 2. This doesn't matter today, but once we enable 52-bit virtual addressing for 4k pages configurations, the vmemmap region may take up almost half of the upper VA region with the current struct page upper bound at 64 bytes. And once we enable KMSAN or other features that push the size of a struct page over 64 bytes, we will run out of VMALLOC space entirely. So instead, let's derive the region size from the actual size of a struct page, and place the entire region 1 GB from the top of the VA space, where it still doesn't share any lower level translation table entries with the fixmap. Acked-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Link: https://lore.kernel.org/r/20231213084024.2367360-14-ardb@google.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Mark Rutland <mark.rutland@arm.com> |
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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.
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.