PROBLEM:  (QARS 71519 71520 69899 58458)    (Patch ID: OSF435-236)
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This patch fixes a problem in which system was consistently crashing by
pressing keys during the transition from firmware callback to OS console
handling.

Stack trace:
   1 panic("kernel memory fault")
   2 trap()
   3 _XentMM()
   4 wsputc()
   5 sccputc()
   6 cnputc()
   7 cons_puts() 
   8 printf()