262bd5724a
Commit
26bfa5f89486 ("x86, amd: Cleanup init_amd")
moved the code that remaps the TSEG region using 4k pages from
init_amd() to bsp_init_amd().
However, bsp_init_amd() is executed well before the direct mapping is
actually created:
setup_arch()
-> early_cpu_init()
-> early_identify_cpu()
-> this_cpu->c_bsp_init()
-> bsp_init_amd()
...
-> init_mem_mapping()
So the change effectively disabled the 4k remapping, because
pfn_range_is_mapped() is always false at this point.
It has been over six years since the commit, and no-one seems to have
noticed this, so just remove the code. The original code was also
incomplete, since it doesn't check how large the TSEG address range
actually is, so it might remap only part of it in any case.
Hygon has copied the incorrect version, so the code has never run on it
since the cpu support was added two years ago. Remove it from there as
well.
Committer notes:
This workaround is incomplete anyway:
1. The code must check MSRC001_0113.TValid (SMM TSeg Mask MSR) first, to
check whether the TSeg address range is enabled.
2. The code must check whether the range is not 2M aligned - if it is,
there's nothing to work around.
3. In all the BIOSes tested, the TSeg range is in a e820 reserved area
and those are not mapped anymore, after
66520ebc2df3 ("x86, mm: Only direct map addresses that are marked as E820_RAM")
which means, there's nothing to be worked around either.
So let's rip it out.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20201127171324.1846019-1-nivedita@alum.mit.edu
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.