230ec83d42
x86_has_pat_wp() is using a wrong test, as it relies on the normal
PAT configuration used by the kernel. In case the PAT MSR has been
setup by another entity (e.g. Xen hypervisor) it might return false
even if the PAT configuration is allowing WP mappings. This due to the
fact that when running as Xen PV guest the PAT MSR is setup by the
hypervisor and cannot be changed by the guest. This results in the WP
related entry to be at a different position when running as Xen PV
guest compared to the bare metal or fully virtualized case.
The correct way to test for WP support is:
1. Get the PTE protection bits needed to select WP mode by reading
__cachemode2pte_tbl[_PAGE_CACHE_MODE_WP] (depending on the PAT MSR
setting this might return protection bits for a stronger mode, e.g.
UC-)
2. Translate those bits back into the real cache mode selected by those
PTE bits by reading __pte2cachemode_tbl[__pte2cm_idx(prot)]
3. Test for the cache mode to be _PAGE_CACHE_MODE_WP
Fixes: f88a68facd9a ("x86/mm: Extend early_memremap() support with additional attrs")
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: <stable@vger.kernel.org> # 4.14
Link: https://lore.kernel.org/r/20220503132207.17234-1-jgross@suse.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.