Make sure that machine check errors with a usable address are properly
marked as poison.

This is needed for errors that occur on memory which have
MCG_STATUS[RIPV] clear - i.e., the interrupted process cannot be
restarted reliably. One example is data poison consumption through the
instruction fetch units on AMD Zen-based systems.

The MF_MUST_KILL flag is passed to memory_failure() when
MCG_STATUS[RIPV] is not set. So the associated process will still be
killed.  What this does, practically, is get rid of one more check to
kill_current_task with the eventual goal to remove it completely.

Also, make the handling identical to what is done on the notifier path
(uc_decode_notifier() does that address usability check too).

The scenario described above occurs when hardware can precisely identify
the address of poisoned memory, but execution cannot reliably continue
for the interrupted hardware thread.

  [ bp: Massage commit message. ]
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20230322005131.174499-1-tony.luck@intel.com