target/ppc: Support directed privileged doorbell interrupt (SDOOR)

BookS msgsndp instruction to self or DPDES register can cause SDOOR
interrupts which crash QEMU with exception not implemented.

Linux does not use msgsndp in SMT1, and KVM only uses DPDES to cause
doorbells when emulating a SMT guest (which is not the default), so
this has gone unnoticed.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20230530130526.372701-1-npiggin@gmail.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

target/ppc/excp_helper.c

@@ -1542,6 +1542,7 @@ static void powerpc_excp_books(PowerPCCPU *cpu, int excp)
     case POWERPC_EXCP_DSEG:      /* Data segment exception                   */
     case POWERPC_EXCP_ISEG:      /* Instruction segment exception            */
     case POWERPC_EXCP_TRACE:     /* Trace exception                          */
+    case POWERPC_EXCP_SDOOR:     /* Doorbell interrupt                       */
         break;
     case POWERPC_EXCP_HISI:      /* Hypervisor instruction storage exception */
         msr |= env->error_code;
@@ -1587,7 +1588,6 @@ static void powerpc_excp_books(PowerPCCPU *cpu, int excp)
     case POWERPC_EXCP_PERFM:     /* Embedded performance monitor interrupt   */
     case POWERPC_EXCP_VPUA:      /* Vector assist exception                  */
     case POWERPC_EXCP_MAINT:     /* Maintenance exception                    */
-    case POWERPC_EXCP_SDOOR:     /* Doorbell interrupt                       */
     case POWERPC_EXCP_HV_MAINT:  /* Hypervisor Maintenance exception         */
         cpu_abort(cs, "%s exception not implemented\n",
                   powerpc_excp_name(excp));