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When paging is enabled, the CR4.PAE and CR4.LA57 control bits cannot be changed, and so they can simply be preserved rather than reason about whether or not they need to be set. CR4.MCE should be preserved unless the kernel was built without CONFIG_X86_MCE, in which case it must be cleared. CR4.PSE should be set explicitly, regardless of whether or not it was set before. CR4.PGE is set explicitly, and then cleared and set again after programming CR3 in order to flush TLB entries based on global translations. This makes the first assignment redundant, and can therefore be omitted. So clear PGE by omitting it from the preserve mask, and set it again explicitly after switching to the new page tables. [ bp: Document the exact operation of CR4.PGE ] Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Tested-by: Tom Lendacky <thomas.lendacky@amd.com> Link: https://lore.kernel.org/r/20240227151907.387873-12-ardb+git@google.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.