tree 2c15630389ad38bb4a7f4e2a1bbbb23723cce211
parent ed399ade3c85adf82fe507339560693e83a27020
author Nicholas Piggin <npiggin@gmail.com> 1710828106 +1000
committer Nicholas Piggin <npiggin@gmail.com> 1711788625 +1000

target/ppc: Do not clear MSR[ME] on MCE interrupts to supervisor

Hardware clears the MSR[ME] bit when delivering a machine check
interrupt, so that is what QEMU does.

The spapr environment runs in supervisor mode though, and receives
machine check interrupts after they are processed by the hypervisor,
and MSR[ME] must always be enabled in supervisor mode (otherwise it
could checkstop the system). So MSR[ME] must not be cleared when
delivering machine checks to the supervisor.

The fix to prevent supervisor mode from modifying MSR[ME] also
prevented it from re-enabling the incorrectly cleared MSR[ME] bit
when returning from handling the interrupt. Before that fix, the
problem was not very noticable with well-behaved code. So the
Fixes tag is not strictly correct, but practically they go together.

Found by kvm-unit-tests machine check tests (not yet upstream).

Fixes: 678b6f1af75ef ("target/ppc: Prevent supervisor from modifying MSR[ME]")
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>