powerpc: Introduce the MSR_S bit

Protected Execution Facility (PEF) is an architectural change for
POWER 9 that enables Secure Virtual Machines (SVMs). When enabled,
PEF adds a new higher privileged mode, called Ultravisor mode, to
POWER architecture.

The hardware changes include the following:

  * There is a new bit in the MSR that determines whether the current
    process is running in secure mode, MSR(S) bit 41. MSR(S)=1, process
    is in secure mode, MSR(s)=0 process is in normal mode.

  * The MSR(S) bit can only be set by the Ultravisor.

  * HRFID cannot be used to set the MSR(S) bit. If the hypervisor needs
    to return to a SVM it must use an ultracall. It can determine if
    the VM it is returning to is secure.

  * The privilege of a process is now determined by three MSR bits,
    MSR(S, HV, PR). In each of the tables below the modes are listed
    from least privilege to highest privilege. The higher privilege
    modes can access all the resources of the lower privilege modes.

    **Secure Mode MSR Settings**

       +---+---+---+---------------+
       | S | HV| PR|Privilege      |
       +===+===+===+===============+
       | 1 | 0 | 1 | Problem       |
       +---+---+---+---------------+
       | 1 | 0 | 0 | Privileged(OS)|
       +---+---+---+---------------+
       | 1 | 1 | 0 | Ultravisor    |
       +---+---+---+---------------+
       | 1 | 1 | 1 | Reserved      |
       +---+---+---+---------------+

    **Normal Mode MSR Settings**

       +---+---+---+---------------+
       | S | HV| PR|Privilege      |
       +===+===+===+===============+
       | 0 | 0 | 1 | Problem       |
       +---+---+---+---------------+
       | 0 | 0 | 0 | Privileged(OS)|
       +---+---+---+---------------+
       | 0 | 1 | 0 | Hypervisor    |
       +---+---+---+---------------+
       | 0 | 1 | 1 | Problem (HV)  |
       +---+---+---+---------------+

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
[ cclaudio: Update the commit message ]
Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190820021326.6884-7-bauerman@linux.ibm.com