KVM: s390: pv: api documentation for asynchronous destroy

Add documentation for the new commands added to the KVM_S390_PV_COMMAND
ioctl.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Nico Boehr <nrb@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20221111170632.77622-3-imbrenda@linux.ibm.com
Message-Id: <20221111170632.77622-3-imbrenda@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

Documentation/virt/kvm/api.rst

@@ -5163,10 +5163,13 @@ KVM_PV_ENABLE
   =====      =============================
 
 KVM_PV_DISABLE
-  Deregister the VM from the Ultravisor and reclaim the memory that
-  had been donated to the Ultravisor, making it usable by the kernel
-  again.  All registered VCPUs are converted back to non-protected
-  ones.
+  Deregister the VM from the Ultravisor and reclaim the memory that had
+  been donated to the Ultravisor, making it usable by the kernel again.
+  All registered VCPUs are converted back to non-protected ones. If a
+  previous protected VM had been prepared for asynchonous teardown with
+  KVM_PV_ASYNC_CLEANUP_PREPARE and not subsequently torn down with
+  KVM_PV_ASYNC_CLEANUP_PERFORM, it will be torn down in this call
+  together with the current protected VM.
 
 KVM_PV_VM_SET_SEC_PARMS
   Pass the image header from VM memory to the Ultravisor in
@@ -5289,6 +5292,36 @@ KVM_PV_DUMP
     authentication tag all of which are needed to decrypt the dump at a
     later time.
 
+KVM_PV_ASYNC_CLEANUP_PREPARE
+  :Capability: KVM_CAP_S390_PROTECTED_ASYNC_DISABLE
+
+  Prepare the current protected VM for asynchronous teardown. Most
+  resources used by the current protected VM will be set aside for a
+  subsequent asynchronous teardown. The current protected VM will then
+  resume execution immediately as non-protected. There can be at most
+  one protected VM prepared for asynchronous teardown at any time. If
+  a protected VM had already been prepared for teardown without
+  subsequently calling KVM_PV_ASYNC_CLEANUP_PERFORM, this call will
+  fail. In that case, the userspace process should issue a normal
+  KVM_PV_DISABLE. The resources set aside with this call will need to
+  be cleaned up with a subsequent call to KVM_PV_ASYNC_CLEANUP_PERFORM
+  or KVM_PV_DISABLE, otherwise they will be cleaned up when KVM
+  terminates. KVM_PV_ASYNC_CLEANUP_PREPARE can be called again as soon
+  as cleanup starts, i.e. before KVM_PV_ASYNC_CLEANUP_PERFORM finishes.
+
+KVM_PV_ASYNC_CLEANUP_PERFORM
+  :Capability: KVM_CAP_S390_PROTECTED_ASYNC_DISABLE
+
+  Tear down the protected VM previously prepared for teardown with
+  KVM_PV_ASYNC_CLEANUP_PREPARE. The resources that had been set aside
+  will be freed during the execution of this command. This PV command
+  should ideally be issued by userspace from a separate thread. If a
+  fatal signal is received (or the process terminates naturally), the
+  command will terminate immediately without completing, and the normal
+  KVM shutdown procedure will take care of cleaning up all remaining
+  protected VMs, including the ones whose teardown was interrupted by
+  process termination.
+
 4.126 KVM_XEN_HVM_SET_ATTR
 --------------------------