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bae3a8d330
Legacy apic init uses bigsmp for smp systems with 8 and more CPUs. The
bigsmp APIC implementation uses physical destination mode, but it
nevertheless initializes LDR and DFR. The LDR even ends up incorrectly with
multiple bit being set.
This does not cause a functional problem because LDR and DFR are ignored
when physical destination mode is active, but it triggered a problem on a
32-bit KVM guest which jumps into a kdump kernel.
The multiple bits set unearthed a bug in the KVM APIC implementation. The
code which creates the logical destination map for VCPUs ignores the
disabled state of the APIC and ends up overwriting an existing valid entry
and as a result, APIC calibration hangs in the guest during kdump
initialization.
Remove the bogus LDR/DFR initialization.
This is not intended to work around the KVM APIC bug. The LDR/DFR
ininitalization is wrong on its own.
The issue goes back into the pre git history. The fixes tag is the commit
in the bitkeeper import which introduced bigsmp support in 2003.
git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Fixes: db7b9e9f26b8 ("[PATCH] Clustered APIC setup for >8 CPU systems")
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20190826101513.5080-2-bsd@redhat.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.