... because interrupts are disabled that early and sending IPIs can
deadlock:

  BUG: sleeping function called from invalid context at kernel/sched/completion.c:99
  in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 0, name: swapper/1
  no locks held by swapper/1/0.
  irq event stamp: 0
  hardirqs last  enabled at (0): [<0000000000000000>] 0x0
  hardirqs last disabled at (0): [<ffffffff8106dda9>] copy_process+0x8b9/0x1ca0
  softirqs last  enabled at (0): [<ffffffff8106dda9>] copy_process+0x8b9/0x1ca0
  softirqs last disabled at (0): [<0000000000000000>] 0x0
  Preemption disabled at:
  [<ffffffff8104703b>] start_secondary+0x3b/0x190
  CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.5.0-rc2+ #1
  Hardware name: GIGABYTE MZ01-CE1-00/MZ01-CE1-00, BIOS F02 08/29/2018
  Call Trace:
   dump_stack
   ___might_sleep.cold.92
   wait_for_completion
   ? generic_exec_single
   rdmsr_safe_on_cpu
   ? wrmsr_on_cpus
   mce_amd_feature_init
   mcheck_cpu_init
   identify_cpu
   identify_secondary_cpu
   smp_store_cpu_info
   start_secondary
   secondary_startup_64

The function smca_configure() is called only on the current CPU anyway,
therefore replace rdmsr_safe_on_cpu() with atomic rdmsr_safe() and avoid
the IPI.

 [ bp: Update commit message. ]
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Yazen Ghannam <yazen.ghannam@amd.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Cc: <stable@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/157252708836.3876.4604398213417262402.stgit@buzz