1 files changed, 3 insertions, 1 deletions

diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt
index 6f362356e738..baa8fde8bd16 100644
--- a/Documentation/kvm/api.txt
+++ b/Documentation/kvm/api.txt
@@ -974,7 +974,9 @@ pending operations.
                         __u32 pad;
                 } hypercall;
 
-Unused.
+Unused.  This was once used for 'hypercall to userspace'.  To implement
+such functionality, use KVM_EXIT_IO (x86) or KVM_EXIT_MMIO (all except s390).
+Note KVM_EXIT_IO is significantly faster than KVM_EXIT_MMIO.
 
                 /* KVM_EXIT_TPR_ACCESS */
                 struct {