tools/kvm_stat: Fix kvm_exit filter name

The filter name is fixed to "exit_reason" for some kvm_exit events, no
matter what architect we have. Actually, the filter name ("exit_reason")
is only applicable to x86, meaning it's broken on other architects
including aarch64.

This fixes the issue by providing various kvm_exit filter names, depending
on architect we're on. Afterwards, the variable filter name is picked and
applied through ioctl(fd, SET_FILTER).

Reported-by: Andrew Jones <[e-mail]>
Signed-off-by: Gavin Shan <[e-mail]>
Cc: [e-mail]
Signed-off-by: Paolo Bonzini <[e-mail]>

tools/kvm/kvm_stat/kvm_stat

···
     def __init__(self, exit_reasons):
         self.sc_perf_evt_open = 298
         self.ioctl_numbers = IOCTL_NUMBERS
+        self.exit_reason_field = 'exit_reason'
         self.exit_reasons = exit_reasons
 
     def debugfs_is_child(self, field):
···
         # numbers depend on the wordsize.
         char_ptr_size = ctypes.sizeof(ctypes.c_char_p)
         self.ioctl_numbers['SET_FILTER'] = 0x80002406 | char_ptr_size << 16
+        self.exit_reason_field = 'exit_nr'
         self.exit_reasons = {}
 
     def debugfs_is_child(self, field):
···
     def __init__(self):
         self.sc_perf_evt_open = 241
         self.ioctl_numbers = IOCTL_NUMBERS
+        self.exit_reason_field = 'esr_ec'
         self.exit_reasons = AARCH64_EXIT_REASONS
 
     def debugfs_is_child(self, field):
···
     def __init__(self):
         self.sc_perf_evt_open = 331
         self.ioctl_numbers = IOCTL_NUMBERS
+        self.exit_reason_field = None
         self.exit_reasons = None
 
     def debugfs_is_child(self, field):
···
         """
         filters = {}
         filters['kvm_userspace_exit'] = ('reason', USERSPACE_EXIT_REASONS)
-        if ARCH.exit_reasons:
-            filters['kvm_exit'] = ('exit_reason', ARCH.exit_reasons)
+        if ARCH.exit_reason_field and ARCH.exit_reasons:
+            filters['kvm_exit'] = (ARCH.exit_reason_field, ARCH.exit_reasons)
         return filters
 
     def _get_available_fields(self):