KVM: Document replacements for KVM_EXIT_HYPERCALL

Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt
index 6f36235..baa8fde 100644 (file)
--- 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 {