For these CPU's, you have to use the ptest operation to search the mmu
tables in order to decide whether it is a real bus error or just a
page fault or write protection violation.
Our old code assumed user space always when calling ptest, and
erroneously assumed the BUSERR bit in the ptest output (mmusr
register) is the only indication for bus errors to check.
In fact, we have to follow a multistage decision tree to decide. 68060
CPUs are much easier to handle correctly.
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