Prevent guest state modifying the MSR[ME] bit. Per ISA:

  An attempt to modify MSRME in privileged but non-hypervisor state is
  ignored (i.e., the bit is not changed).

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 target/ppc/helper_regs.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/target/ppc/helper_regs.c b/target/ppc/helper_regs.c
index e0b2dcd02e..bd17c14136 100644
--- a/target/ppc/helper_regs.c
+++ b/target/ppc/helper_regs.c
@@ -264,6 +264,11 @@ int hreg_store_msr(CPUPPCState *env, target_ulong value, int alter_hv)
         value &= ~MSR_HVB;
         value |= env->msr & MSR_HVB;
     }
+    /* Attempt to modify MSR[ME] in guest state is ignored */
+    if (is_book3s_arch2x(env) && !(env->msr & MSR_HVB)) {
+        value &= ~(1 << MSR_ME);
+        value |= env->msr & (1 << MSR_ME);
+    }
     if ((value ^ env->msr) & (R_MSR_IR_MASK | R_MSR_DR_MASK)) {
         cpu_interrupt_exittb(cs);
     }
-- 
2.42.0