hw/ppc: Take QEMU lock when calling ppc_dcr_read/write()

The ppc_dcr_read() and ppc_dcr_write() functions call into callbacks
in device code, so we need to hold the QEMU iothread lock while
calling them.  This is the case already for the callsites in
kvmppc_handle_dcr_read/write(), but we must also take the lock when
calling the helpers from TCG.

This fixes a bug where attempting to initialise the PPC405EP
SDRAM will cause an assertion when sdram_map_bcr() attempts
to remap memory regions.

Reported-by: Amit Lazar <abasarlaz@hotmail.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20200322192258.14039-1-peter.maydell@linaro.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

target/ppc/timebase_helper.c

@@ -21,6 +21,7 @@
 #include "exec/helper-proto.h"
 #include "exec/exec-all.h"
 #include "qemu/log.h"
+#include "qemu/main-loop.h"
 
 /*****************************************************************************/
 /* SPR accesses */
@@ -167,13 +168,19 @@ target_ulong helper_load_dcr(CPUPPCState *env, target_ulong dcrn)
         raise_exception_err_ra(env, POWERPC_EXCP_PROGRAM,
                                POWERPC_EXCP_INVAL |
                                POWERPC_EXCP_INVAL_INVAL, GETPC());
-    } else if (unlikely(ppc_dcr_read(env->dcr_env,
-                                     (uint32_t)dcrn, &val) != 0)) {
-        qemu_log_mask(LOG_GUEST_ERROR, "DCR read error %d %03x\n",
-                      (uint32_t)dcrn, (uint32_t)dcrn);
-        raise_exception_err_ra(env, POWERPC_EXCP_PROGRAM,
-                               POWERPC_EXCP_INVAL |
-                               POWERPC_EXCP_PRIV_REG, GETPC());
+    } else {
+        int ret;
+
+        qemu_mutex_lock_iothread();
+        ret = ppc_dcr_read(env->dcr_env, (uint32_t)dcrn, &val);
+        qemu_mutex_unlock_iothread();
+        if (unlikely(ret != 0)) {
+            qemu_log_mask(LOG_GUEST_ERROR, "DCR read error %d %03x\n",
+                          (uint32_t)dcrn, (uint32_t)dcrn);
+            raise_exception_err_ra(env, POWERPC_EXCP_PROGRAM,
+                                   POWERPC_EXCP_INVAL |
+                                   POWERPC_EXCP_PRIV_REG, GETPC());
+        }
     }
     return val;
 }
@@ -185,12 +192,17 @@ void helper_store_dcr(CPUPPCState *env, target_ulong dcrn, target_ulong val)
         raise_exception_err_ra(env, POWERPC_EXCP_PROGRAM,
                                POWERPC_EXCP_INVAL |
                                POWERPC_EXCP_INVAL_INVAL, GETPC());
-    } else if (unlikely(ppc_dcr_write(env->dcr_env, (uint32_t)dcrn,
-                                      (uint32_t)val) != 0)) {
-        qemu_log_mask(LOG_GUEST_ERROR, "DCR write error %d %03x\n",
-                      (uint32_t)dcrn, (uint32_t)dcrn);
-        raise_exception_err_ra(env, POWERPC_EXCP_PROGRAM,
-                               POWERPC_EXCP_INVAL |
-                               POWERPC_EXCP_PRIV_REG, GETPC());
+    } else {
+        int ret;
+        qemu_mutex_lock_iothread();
+        ret = ppc_dcr_write(env->dcr_env, (uint32_t)dcrn, (uint32_t)val);
+        qemu_mutex_unlock_iothread();
+        if (unlikely(ret != 0)) {
+            qemu_log_mask(LOG_GUEST_ERROR, "DCR write error %d %03x\n",
+                          (uint32_t)dcrn, (uint32_t)dcrn);
+            raise_exception_err_ra(env, POWERPC_EXCP_PROGRAM,
+                                   POWERPC_EXCP_INVAL |
+                                   POWERPC_EXCP_PRIV_REG, GETPC());
+        }
     }
 }