powerpc/vas: Define nx_fault_stamp in coprocessor_request_block

Kernel sets fault address and status in CRB for NX page fault on user
space address after processing page fault. User space gets the signal
and handles the fault mentioned in CRB by bringing the page in to
memory and send NX request again.
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1587016769.2275.1048.camel@hbabu-laptop

arch/powerpc/include/asm/icswx.h

@@ -108,6 +108,17 @@ struct data_descriptor_entry {
 	__be64 address;
 } __packed __aligned(DDE_ALIGN);
 
+/* 4.3.2 NX-stamped Fault CRB */
+
+#define NX_STAMP_ALIGN          (0x10)
+
+struct nx_fault_stamp {
+	__be64 fault_storage_addr;
+	__be16 reserved;
+	__u8   flags;
+	__u8   fault_status;
+	__be32 pswid;
+} __packed __aligned(NX_STAMP_ALIGN);
 
 /* Chapter 6.5.2 Coprocessor-Request Block (CRB) */
 
@@ -135,10 +146,15 @@ struct coprocessor_request_block {
 
 	struct coprocessor_completion_block ccb;
 
-	u8 reserved[48];
+	union {
+		struct nx_fault_stamp nx;
+		u8 reserved[16];
+	} stamp;
+
+	u8 reserved[32];
 
 	struct coprocessor_status_block csb;
-} __packed __aligned(CRB_ALIGN);
+} __packed;
 
 
 /* RFC02167 Initiate Coprocessor Instructions document