KVM: add doc note about PIO/MMIO completion API
Document that partially emulated instructions leave the guest state
inconsistent, and that the kernel will complete operations before
checking for pending signals.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt
index c6416a3..beb444a 100644
--- a/Documentation/kvm/api.txt
+++ b/Documentation/kvm/api.txt
@@ -820,6 +820,13 @@
by kvm. The 'data' member contains the written data if 'is_write' is
true, and should be filled by application code otherwise.
+NOTE: For KVM_EXIT_IO and KVM_EXIT_MMIO, the corresponding operations
+are complete (and guest state is consistent) only after userspace has
+re-entered the kernel with KVM_RUN. The kernel side will first finish
+incomplete operations and then check for pending signals. Userspace
+can re-enter the guest with an unmasked signal pending to complete
+pending operations.
+
/* KVM_EXIT_HYPERCALL */
struct {
__u64 nr;