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David Woodhouse 06a0e2a320 x86/kexec: Allocate PGD for x86_64 transition page tables separately 
[ Upstream commit 4b5bc2ec9a ]

Now that the following fix:

  d0ceea662d ("x86/mm: Add _PAGE_NOPTISHADOW bit to avoid updating userspace page tables")

stops kernel_ident_mapping_init() from scribbling over the end of a
4KiB PGD by assuming the following 4KiB will be a userspace PGD,
there's no good reason for the kexec PGD to be part of a single
8KiB allocation with the control_code_page.

( It's not clear that that was the reason for x86_64 kexec doing it that
  way in the first place either; there were no comments to that effect and
  it seems to have been the case even before PTI came along. It looks like
  it was just a happy accident which prevented memory corruption on kexec. )

Either way, it definitely isn't needed now. Just allocate the PGD
separately on x86_64, like i386 already does.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20241205153343.3275139-6-dwmw2@infradead.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-02-17 10:04:54 +01:00
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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 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.