The unimplemented movdqa (66 0f 7f 07) instruction triggers a bug in
the x86 emulator. The emulator should fail since the instruction is
unimplemented. However the emulator thinks it is succeeding but we
keep re-executing the same instruction over and over. top shows 100%
CPU utilization and perf top shows we're constantly running through
the x86 emulator in kvm.ko.
The problem is that ctxt->d != 0 even though the instruction is
unimplemented (N):
while (ctxt->d & GroupMask) {
switch (ctxt->d & GroupMask) {
... <-- opcode zeroed if instruction is unimplemented
}
ctxt->d &= ~(u64)GroupMask; <-- only clears GroupMask
ctxt->d |= opcode.flags; <-- opcode.flags == 0, ctxt->d != 0
}
...
/* Unrecognised? */
if (ctxt->d == 0 || (ctxt->d & Undefined)) <-- always false
return EMULATION_FAILED;
Stefan
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