sparc32 do_unassigned_access overhaul v2

According to pages 9-31 - 9-34 of "SuperSPARC & MultiCache Controller
User's Manual":

1. "A lower priority fault may not overwrite the
    MFSR status of a higher priority fault."
2. The MFAR is overwritten according to the policy defined for the MFSR
3. The overwrite bit is asserted if the fault status register (MFSR)
   has been written more than once by faults of the same class
4. SuperSPARC will never place instruction fault addresses in the MFAR.

Implementation of points 1-3 allows booting Solaris 2.6 and 2.5.1.

v2: CODING_STYLE fixes
Signed-off-by: NArtyom Tarasenko <atar4qemu@gmail.com>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

target-sparc/op_helper.c

@@ -3714,6 +3714,7 @@ void do_unassigned_access(target_phys_addr_t addr, int is_write, int is_exec,
                           int is_asi, int size)
 {
     CPUState *saved_env;
+    int fault_type;
 
     /* XXX: hack to restore env in all cases, even if not called from
        generated code */
@@ -3731,18 +3732,29 @@ void do_unassigned_access(target_phys_addr_t addr, int is_write, int is_exec,
                is_exec ? "exec" : is_write ? "write" : "read", size,
                size == 1 ? "" : "s", addr, env->pc);
 #endif
-    if (env->mmuregs[3]) /* Fault status register */
-        env->mmuregs[3] = 1; /* overflow (not read before another fault) */
-    if (is_asi)
-        env->mmuregs[3] |= 1 << 16;
-    if (env->psrs)
-        env->mmuregs[3] |= 1 << 5;
-    if (is_exec)
-        env->mmuregs[3] |= 1 << 6;
-    if (is_write)
-        env->mmuregs[3] |= 1 << 7;
-    env->mmuregs[3] |= (5 << 2) | 2;
-    env->mmuregs[4] = addr; /* Fault address register */
+    /* Don't overwrite translation and access faults */
+    fault_type = (env->mmuregs[3] & 0x1c) >> 2;
+    if ((fault_type > 4) || (fault_type == 0)) {
+        env->mmuregs[3] = 0; /* Fault status register */
+        if (is_asi)
+            env->mmuregs[3] |= 1 << 16;
+        if (env->psrs)
+            env->mmuregs[3] |= 1 << 5;
+        if (is_exec)
+            env->mmuregs[3] |= 1 << 6;
+        if (is_write)
+            env->mmuregs[3] |= 1 << 7;
+        env->mmuregs[3] |= (5 << 2) | 2;
+        /* SuperSPARC will never place instruction fault addresses in the FAR */
+        if (!is_exec) {
+            env->mmuregs[4] = addr; /* Fault address register */
+        }
+    }
+    /* overflow (same type fault was not read before another fault) */
+    if (fault_type == ((env->mmuregs[3] & 0x1c)) >> 2) {
+        env->mmuregs[3] |= 1;
+    }
+
     if ((env->mmuregs[0] & MMU_E) && !(env->mmuregs[0] & MMU_NF)) {
         if (is_exec)
             raise_exception(TT_CODE_ACCESS);
@@ -3750,6 +3762,12 @@ void do_unassigned_access(target_phys_addr_t addr, int is_write, int is_exec,
             raise_exception(TT_DATA_ACCESS);
     }
     env = saved_env;
+
+    /* flush neverland mappings created during no-fault mode,
+       so the sequential MMU faults report proper fault types */
+    if (env->mmuregs[0] & MMU_NF) {
+        tlb_flush(env, 1);
+    }
 }
 #else
 void do_unassigned_access(target_phys_addr_t addr, int is_write, int is_exec,