bb99836199
The CR3 restore happens in:
1. #NMI return.
2. paranoid_exit() (i.e. #MCE, #VC, #DB and #DF return)
Contrary to the implication in commit 21e9445911 ("x86/mm: Optimize
RESTORE_CR3"), the kernel never modifies CR3 in any of these exceptions,
except for switching from user to kernel pagetables under PTI. That
means that most of the time when returning from an exception that
interrupted the kernel no CR3 restore is necessary. Writing CR3 is
expensive on some machines.
Most of the time because the interrupt might have come during kernel entry
before the user to kernel CR3 switch or the during exit after the kernel to
user switch. In the former case skipping the restore would be correct, but
definitely not for the latter.
So check the saved CR3 value and restore it only, if it is a user CR3.
Give the macro a new name to clarify its usage, and remove a comment that
was describing the original behaviour along with the not longer needed jump
label.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240108113950.360438-1-jackmanb@google.com
[Rewrote commit message; responded to review comments]
Change-Id: I6e56978c4753fb943a7897ff101f519514fa0827
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.