On 11/1/23 18:36, Sean Christopherson wrote:
A good example is KVM_RUN with -EINTR; if KVM were to return something other than -EINTR on a pending signal or vcpu->run->immediate_exit, userspace would fall over.
And dually if KVM were to return KVM_EXIT_INTR together with something other than -EINTR.
And purging exit_reason super early is subtly tricky because KVM's (again, poorly documented) ABI is that *some* exit reasons are preserved across KVM_RUN with vcpu->run->immediate_exit (or with a pending signal). https://lore.kernel.org/all/ZFFbwOXZ5uI%2Fgdaf@xxxxxxxxxx
vcpu->run->immediate_exit preserves all exit reasons, but it's not a good idea that immediate_exit behaves different from a pending signal on entry to KVM_RUN (remember that immediate_exit was meant to be a better performing alternative to KVM_SET_SIGNAL_MASK).
In principle, vcpu->run->immediate_exit could return KVM_EXIT_INTR (perhaps even _should_, except that breaks selftests so at this point it is ABI).
Paolo
