powerpc: Disable Collaborative Memory Manager for kdump

powerpc: Disable Collaborative Memory Manager for kdump

commit 2218108e182fd8a6d9106077833ed7ad05fc8e75 upstream.

When running Active Memory Sharing, the Collaborative Memory Manager
(CMM) may mark some pages as "loaned" with the hypervisor.
Periodically, the CMM will query the hypervisor for a loan request,
which is a single signed value.  When kexec'ing into a kdump kernel,
the CMM driver in the kdump kernel is not aware of the pages the
previous kernel had marked as "loaned", so the hypervisor and the CMM
driver are out of sync.  This results in the CMM driver getting a
negative loan request, which can then get treated as a large unsigned
value and can cause kdump to hang due to the CMM driver inflating too
large.  Since there really is no clean way for the CMM driver in the
kdump kernel to clean this up, simply disable CMM in the kdump kernel.
This fixes hangs we were seeing doing kdump with AMS.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>