KVM: PPC: Book3S HV: Track the state GFNs associated with secure VMs

During the life of SVM, its GFNs transition through normal, secure and
shared states. Since the kernel does not track GFNs that are shared, it
is not possible to disambiguate a shared GFN from a GFN whose PFN has
not yet been migrated to a secure-PFN. Also it is not possible to
disambiguate a secure-GFN from a GFN whose GFN has been pagedout from
the ultravisor.

The ability to identify the state of a GFN is needed to skip migration
of its PFN to secure-PFN during ESM transition.

The code is re-organized to track the states of a GFN as explained
below.

************************************************************************
 1. States of a GFN
    ---------------
 The GFN can be in one of the following states.

 (a) Secure - The GFN is secure. The GFN is associated with
 	a Secure VM, the contents of the GFN is not accessible
 	to the Hypervisor.  This GFN can be backed by a secure-PFN,
 	or can be backed by a normal-PFN with contents encrypted.
 	The former is true when the GFN is paged-in into the
 	ultravisor. The latter is true when the GFN is paged-out
 	of the ultravisor.

 (b) Shared - The GFN is shared. The GFN is associated with a
 	a secure VM. The contents of the GFN is accessible to
 	Hypervisor. This GFN is backed by a normal-PFN and its
 	content is un-encrypted.

 (c) Normal - The GFN is a normal. The GFN is associated with
 	a normal VM. The contents of the GFN is accesible to
 	the Hypervisor. Its content is never encrypted.

 2. States of a VM.
    ---------------

 (a) Normal VM:  A VM whose contents are always accessible to
 	the hypervisor.  All its GFNs are normal-GFNs.

 (b) Secure VM: A VM whose contents are not accessible to the
 	hypervisor without the VM's consent.  Its GFNs are
 	either Shared-GFN or Secure-GFNs.

 (c) Transient VM: A Normal VM that is transitioning to secure VM.
 	The transition starts on successful return of
 	H_SVM_INIT_START, and ends on successful return
 	of H_SVM_INIT_DONE. This transient VM, can have GFNs
 	in any of the three states; i.e Secure-GFN, Shared-GFN,
 	and Normal-GFN.	The VM never executes in this state
 	in supervisor-mode.

 3. Memory slot State.
    ------------------
  	The state of a memory slot mirrors the state of the
  	VM the memory slot is associated with.

 4. VM State transition.
    --------------------

  A VM always starts in Normal Mode.

  H_SVM_INIT_START moves the VM into transient state. During this
  time the Ultravisor may request some of its GFNs to be shared or
  secured. So its GFNs can be in one of the three GFN states.

  H_SVM_INIT_DONE moves the VM entirely from transient state to
  secure-state. At this point any left-over normal-GFNs are
  transitioned to Secure-GFN.

  H_SVM_INIT_ABORT moves the transient VM back to normal VM.
  All its GFNs are moved to Normal-GFNs.

  UV_TERMINATE transitions the secure-VM back to normal-VM. All
  the secure-GFN and shared-GFNs are tranistioned to normal-GFN
  Note: The contents of the normal-GFN is undefined at this point.

 5. GFN state implementation:
    -------------------------

 Secure GFN is associated with a secure-PFN; also called uvmem_pfn,
 when the GFN is paged-in. Its pfn[] has KVMPPC_GFN_UVMEM_PFN flag
 set, and contains the value of the secure-PFN.
 It is associated with a normal-PFN; also called mem_pfn, when
 the GFN is pagedout. Its pfn[] has KVMPPC_GFN_MEM_PFN flag set.
 The value of the normal-PFN is not tracked.

 Shared GFN is associated with a normal-PFN. Its pfn[] has
 KVMPPC_UVMEM_SHARED_PFN flag set. The value of the normal-PFN
 is not tracked.

 Normal GFN is associated with normal-PFN. Its pfn[] has
 no flag set. The value of the normal-PFN is not tracked.

 6. Life cycle of a GFN
    --------------------
 --------------------------------------------------------------
 |        |     Share  |  Unshare | SVM       |H_SVM_INIT_DONE|
 |        |operation   |operation | abort/    |               |
 |        |            |          | terminate |               |
 -------------------------------------------------------------
 |        |            |          |           |               |
 | Secure |     Shared | Secure   |Normal     |Secure         |
 |        |            |          |           |               |
 | Shared |     Shared | Secure   |Normal     |Shared         |
 |        |            |          |           |               |
 | Normal |     Shared | Secure   |Normal     |Secure         |
 --------------------------------------------------------------

 7. Life cycle of a VM
    --------------------
 --------------------------------------------------------------------
 |         |  start    |  H_SVM_  |H_SVM_   |H_SVM_     |UV_SVM_    |
 |         |  VM       |INIT_START|INIT_DONE|INIT_ABORT |TERMINATE  |
 |         |           |          |         |           |           |
 --------- ----------------------------------------------------------
 |         |           |          |         |           |           |
 | Normal  | Normal    | Transient|Error    |Error      |Normal     |
 |         |           |          |         |           |           |
 | Secure  |   Error   | Error    |Error    |Error      |Normal     |
 |         |           |          |         |           |           |
 |Transient|   N/A     | Error    |Secure   |Normal     |Normal     |
 --------------------------------------------------------------------

************************************************************************
Reviewed-by: Bharata B Rao <bharata@linux.ibm.com>
Reviewed-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>