1dbc0a9515
The intent of the sign games was to not modify kernel addresses when
untagging them. However, that had two issues:
(a) it didn't actually work as intended, since the mask was calculated
as 'addr >> 63' on an _unsigned_ address. So instead of getting a
mask of all ones for kernel addresses, you just got '1'.
(b) untagging a kernel address isn't actually a valid operation anyway.
Now, (a) had originally been true for both 'untagged_addr()' and the
remote version of it, but had accidentally been fixed for the regular
version of untagged_addr() by commit e0bddc19ba95 ("x86/mm: Reduce
untagged_addr() overhead for systems without LAM"). That one rewrote
the shift to be part of the alternative asm code, and in the process
changed the unsigned shift into a signed 'sar' instruction.
And while it is true that we don't want to turn what looks like a kernel
address into a user address by masking off the high bit, that doesn't
need these sign masking games - all it needs is that the mm context
'untag_mask' value has the high bit set.
Which it always does.
So simplify the code by just removing the superfluous (and in the case
of untagged_addr_remote(), still buggy) sign bit games in the address
masking.
Acked-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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.