x86: fix crash due to missing debugctlmsr on AMD K6-3
currently if you use PTRACE_SINGLEBLOCK on AMD K6-3 (i586) it will crash.
Kernel now wrongly assumes existing DEBUGCTLMSR MSR register there.
Removed the assumption also for some other non-K6 CPUs but I am not sure there
(but it can only bring small inefficiency there if my assumption is wrong).
Based on info from Roland McGrath, Chuck Ebbert and Mikulas Patocka.
More info at:
https://bugzilla.redhat.com/show_bug.cgi?id=456175
Signed-off-by: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Jan Kratochvil