target/ppc: Fix regression in Radix MMU

Commit 47e83d9 ended up unintentionally changing the control flow
of ppc_radix64_process_scoped_xlate(). When guest_visible is false,
it must not raise an exception, even if the radix configuration is
not valid.

This regression prevented Linux boot in a nested environment with
L1 using TCG and emulating KVM (cap-nested-hv=on) and L2 using
KVM. L2 would hang on Linux's futex_init(), when it tested how a
futex_atomic_cmpxchg_inatomic() handled a fault, because L1 would
start a loop of trying to perform partition scoped translations
and raising exceptions.

Fixes: 47e83d9 ("target/ppc: Improve Radix xlate level validation")
Reported-by: Victor Colombo <victor.colombo@eldorado.org.br>
Signed-off-by: Leandro Lupori <leandro.lupori@eldorado.org.br>
Tested-by: Víctor Colombo <victor.colombo@eldorado.org.br>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20221028183617.121786-1-leandro.lupori@eldorado.org.br>
[danielhb: use %"PRIu64" to print 'nls']
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

target/ppc/mmu-radix64.c

@@ -238,6 +238,8 @@ static void ppc_radix64_set_rc(PowerPCCPU *cpu, MMUAccessType access_type,
 
 static bool ppc_radix64_is_valid_level(int level, int psize, uint64_t nls)
 {
+    bool ret;
+
     /*
      * Check if this is a valid level, according to POWER9 and POWER10
      * Processor User's Manuals, sections 4.10.4.1 and 5.10.6.1, respectively:
@@ -249,16 +251,25 @@ static bool ppc_radix64_is_valid_level(int level, int psize, uint64_t nls)
      */
     switch (level) {
     case 0:     /* Root Page Dir */
-        return psize == 52 && nls == 13;
+        ret = psize == 52 && nls == 13;
+        break;
     case 1:
     case 2:
-        return nls == 9;
+        ret = nls == 9;
+        break;
     case 3:
-        return nls == 9 || nls == 5;
+        ret = nls == 9 || nls == 5;
+        break;
     default:
-        qemu_log_mask(LOG_GUEST_ERROR, "invalid radix level: %d\n", level);
-        return false;
+        ret = false;
+    }
+
+    if (unlikely(!ret)) {
+        qemu_log_mask(LOG_GUEST_ERROR, "invalid radix configuration: "
+                      "level %d size %d nls %"PRIu64"\n",
+                      level, psize, nls);
     }
+    return ret;
 }
 
 static int ppc_radix64_next_level(AddressSpace *as, vaddr eaddr,
@@ -519,11 +530,13 @@ static int ppc_radix64_process_scoped_xlate(PowerPCCPU *cpu,
 
             if (!ppc_radix64_is_valid_level(level++, *g_page_size, nls)) {
                 fault_cause |= DSISR_R_BADCONFIG;
-                return 1;
+                ret = 1;
+            } else {
+                ret = ppc_radix64_next_level(cs->as, eaddr & R_EADDR_MASK,
+                                             &h_raddr, &nls, g_page_size,
+                                             &pte, &fault_cause);
             }
 
-            ret = ppc_radix64_next_level(cs->as, eaddr & R_EADDR_MASK, &h_raddr,
-                                         &nls, g_page_size, &pte, &fault_cause);
             if (ret) {
                 /* No valid pte */
                 if (guest_visible) {