x86/sgx: Define error codes for use by ENCLS[EUPDATESVN]

Add error codes for ENCLS[EUPDATESVN], then SGX CPUSVN update process can
know the execution state of EUPDATESVN and notify userspace.

EUPDATESVN will be called when no active SGX users is guaranteed. Only add
the error codes that can legally happen. E.g., it could also fail due to
"SGX not ready" when there's SGX users but it wouldn't happen in this
implementation.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: Nataliia Bondarevska <bondarn@google.com>

Author: ereshetova

arch/x86/include/asm/sgx.h

@@ -73,6 +73,10 @@ enum sgx_encls_function {
  *				public key does not match IA32_SGXLEPUBKEYHASH.
  * %SGX_PAGE_NOT_MODIFIABLE:	The EPC page cannot be modified because it
  *				is in the PENDING or MODIFIED state.
+ * %SGX_INSUFFICIENT_ENTROPY:	Insufficient entropy in RNG.
+ * %SGX_NO_UPDATE:		EUPDATESVN could not update the CPUSVN because the
+ *				current SVN was not newer than CPUSVN. This is the most
+ *				common error code returned by EUPDATESVN.
  * %SGX_UNMASKED_EVENT:		An unmasked event, e.g. INTR, was received
  */
 enum sgx_return_code {
@@ -81,6 +85,8 @@ enum sgx_return_code {
 	SGX_CHILD_PRESENT		= 13,
 	SGX_INVALID_EINITTOKEN		= 16,
 	SGX_PAGE_NOT_MODIFIABLE		= 20,
+	SGX_INSUFFICIENT_ENTROPY	= 29,
+	SGX_NO_UPDATE			= 31,
 	SGX_UNMASKED_EVENT		= 128,
 };