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09794f6893
SWAPGS is no longer needed thus NOT allowed with FRED because FRED
transitions ensure that an operating system can _always_ operate
with its own GS base address:
- For events that occur in ring 3, FRED event delivery swaps the GS
base address with the IA32_KERNEL_GS_BASE MSR.
- ERETU (the FRED transition that returns to ring 3) also swaps the
GS base address with the IA32_KERNEL_GS_BASE MSR.
And the operating system can still setup the GS segment for a user
thread without the need of loading a user thread GS with:
- Using LKGS, available with FRED, to modify other attributes of the
GS segment without compromising its ability always to operate with
its own GS base address.
- Accessing the GS segment base address for a user thread as before
using RDMSR or WRMSR on the IA32_KERNEL_GS_BASE MSR.
Note, LKGS loads the GS base address into the IA32_KERNEL_GS_BASE MSR
instead of the GS segment's descriptor cache. As such, the operating
system never changes its runtime GS base address.
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Shan Kang <shan.kang@intel.com>
Link: https://lore.kernel.org/r/20231205105030.8698-19-xin3.li@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.