docs: trusted-encryped: add PKWM as a new trust source

Update Documentation/security/keys/trusted-encrypted.rst and Documentation/
admin-guide/kernel-parameters.txt with PowerVM Key Wrapping Module (PKWM)
as a new trust source

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Signed-off-by: Srish Srinivasan <ssrish@linux.ibm.com>
Tested-by: Nayna Jain <nayna@linux.ibm.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260127145228.48320-7-ssrish@linux.ibm.com

Documentation/admin-guide/kernel-parameters.txt

@@ -7755,6 +7755,7 @@ Kernel parameters
 			- "tee"
 			- "caam"
 			- "dcp"
+			- "pkwm"
 			If not specified then it defaults to iterating through
 			the trust source list starting with TPM and assigns the
 			first trust source as a backend which is initialized

Documentation/security/keys/trusted-encrypted.rst

@@ -81,6 +81,14 @@ safe.
          and the UNIQUE key. Default is to use the UNIQUE key, but selecting
          the OTP key can be done via a module parameter (dcp_use_otp_key).
 
+     (5) PKWM (PowerVM Key Wrapping Module: IBM PowerVM + Platform KeyStore)
+
+         Rooted to a unique, per-LPAR key, which is derived from a system-wide,
+         randomly generated LPAR root key. Both the per-LPAR keys and the LPAR
+         root key are stored in hypervisor-owned secure memory at runtime,
+         and the LPAR root key is additionally persisted in secure locations
+         such as the processor SEEPROMs and encrypted NVRAM.
+
   *  Execution isolation
 
      (1) TPM
@@ -102,6 +110,14 @@ safe.
          environment. Only basic blob key encryption is executed there.
          The actual key sealing/unsealing is done on main processor/kernel space.
 
+     (5) PKWM (PowerVM Key Wrapping Module: IBM PowerVM + Platform KeyStore)
+
+         Fixed set of cryptographic operations done on on-chip hardware
+         cryptographic acceleration unit NX. Keys for wrapping and unwrapping
+         are managed by PowerVM Platform KeyStore, which stores keys in an
+         isolated in-memory copy in secure hypervisor memory, as well as in a
+         persistent copy in hypervisor-encrypted NVRAM.
+
   * Optional binding to platform integrity state
 
      (1) TPM
@@ -129,6 +145,11 @@ safe.
          Relies on Secure/Trusted boot process (called HAB by vendor) for
          platform integrity.
 
+     (5) PKWM (PowerVM Key Wrapping Module: IBM PowerVM + Platform KeyStore)
+
+         Relies on secure and trusted boot process of IBM Power systems for
+         platform integrity.
+
   *  Interfaces and APIs
 
      (1) TPM
@@ -149,6 +170,11 @@ safe.
          Vendor-specific API that is implemented as part of the DCP crypto driver in
          ``drivers/crypto/mxs-dcp.c``.
 
+     (5) PKWM (PowerVM Key Wrapping Module: IBM PowerVM + Platform KeyStore)
+
+         Platform Keystore has well documented interfaces in PAPR document.
+         Refer to ``Documentation/arch/powerpc/papr_hcalls.rst``
+
   *  Threat model
 
      The strength and appropriateness of a particular trust source for a given
@@ -191,6 +217,10 @@ selected trust source:
      a dedicated hardware RNG that is independent from DCP which can be enabled
      to back the kernel RNG.
 
+   * PKWM (PowerVM Key Wrapping Module: IBM PowerVM + Platform KeyStore)
+
+     The normal kernel random number generator is used to generate keys.
+
 Users may override this by specifying ``trusted.rng=kernel`` on the kernel
 command-line to override the used RNG with the kernel's random number pool.
 
@@ -321,6 +351,26 @@ Usage::
 specific to this DCP key-blob implementation.  The key length for new keys is
 always in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
 
+Trusted Keys usage: PKWM
+------------------------
+
+Usage::
+
+    keyctl add trusted name "new keylen [options]" ring
+    keyctl add trusted name "load hex_blob" ring
+    keyctl print keyid
+
+    options:
+       wrap_flags=   ascii hex value of security policy requirement
+                       0x00: no secure boot requirement (default)
+                       0x01: require secure boot to be in either audit or
+                             enforced mode
+                       0x02: require secure boot to be in enforced mode
+
+"keyctl print" returns an ASCII hex copy of the sealed key, which is in format
+specific to PKWM key-blob implementation.  The key length for new keys is
+always in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
+
 Encrypted Keys usage
 --------------------