diff --git a/target/arm/ptw.c b/target/arm/ptw.c
index b0f8c59767..437f6fefa9 100644
--- a/target/arm/ptw.c
+++ b/target/arm/ptw.c
@@ -1077,70 +1077,119 @@ static ARMVAParameters aa32_va_parameters(CPUARMState *env, uint32_t va,
  * check_s2_mmu_setup
  * @cpu:        ARMCPU
  * @is_aa64:    True if the translation regime is in AArch64 state
- * @startlevel: Suggested starting level
- * @inputsize:  Bitsize of IPAs
+ * @tcr:        VTCR_EL2 or VSTCR_EL2
+ * @ds:         Effective value of TCR.DS.
+ * @iasize:     Bitsize of IPAs
  * @stride:     Page-table stride (See the ARM ARM)
  *
- * Returns true if the suggested S2 translation parameters are OK and
- * false otherwise.
+ * Decode the starting level of the S2 lookup, returning INT_MIN if
+ * the configuration is invalid.
  */
-static bool check_s2_mmu_setup(ARMCPU *cpu, bool is_aa64, int level,
-                               int inputsize, int stride, int outputsize)
+static int check_s2_mmu_setup(ARMCPU *cpu, bool is_aa64, uint64_t tcr,
+                              bool ds, int iasize, int stride)
 {
-    const int grainsize = stride + 3;
-    int startsizecheck;
-
-    /*
-     * Negative levels are usually not allowed...
-     * Except for FEAT_LPA2, 4k page table, 52-bit address space, which
-     * begins with level -1.  Note that previous feature tests will have
-     * eliminated this combination if it is not enabled.
-     */
-    if (level < (inputsize == 52 && stride == 9 ? -1 : 0)) {
-        return false;
-    }
-
-    startsizecheck = inputsize - ((3 - level) * stride + grainsize);
-    if (startsizecheck < 1 || startsizecheck > stride + 4) {
-        return false;
-    }
+    int sl0, sl2, startlevel, granulebits, levels;
+    int s1_min_iasize, s1_max_iasize;
 
+    sl0 = extract32(tcr, 6, 2);
     if (is_aa64) {
+        /*
+         * AArch64.S2InvalidTxSZ: While we checked tsz_oob near the top of
+         * get_phys_addr_lpae, that used aa64_va_parameters which apply
+         * to aarch64.  If Stage1 is aarch32, the min_txsz is larger.
+         * See AArch64.S2MinTxSZ, where min_tsz is 24, translated to
+         * inputsize is 64 - 24 = 40.
+         */
+        if (iasize < 40 && !arm_el_is_aa64(&cpu->env, 1)) {
+            goto fail;
+        }
+
+        /*
+         * AArch64.S2InvalidSL: Interpretation of SL depends on the page size,
+         * so interleave AArch64.S2StartLevel.
+         */
         switch (stride) {
-        case 13: /* 64KB Pages.  */
-            if (level == 0 || (level == 1 && outputsize <= 42)) {
-                return false;
+        case 9: /* 4KB */
+            /* SL2 is RES0 unless DS=1 & 4KB granule. */
+            sl2 = extract64(tcr, 33, 1);
+            if (ds && sl2) {
+                if (sl0 != 0) {
+                    goto fail;
+                }
+                startlevel = -1;
+            } else {
+                startlevel = 2 - sl0;
+                switch (sl0) {
+                case 2:
+                    if (arm_pamax(cpu) < 44) {
+                        goto fail;
+                    }
+                    break;
+                case 3:
+                    if (!cpu_isar_feature(aa64_st, cpu)) {
+                        goto fail;
+                    }
+                    startlevel = 3;
+                    break;
+                }
             }
             break;
-        case 11: /* 16KB Pages.  */
-            if (level == 0 || (level == 1 && outputsize <= 40)) {
-                return false;
+        case 11: /* 16KB */
+            switch (sl0) {
+            case 2:
+                if (arm_pamax(cpu) < 42) {
+                    goto fail;
+                }
+                break;
+            case 3:
+                if (!ds) {
+                    goto fail;
+                }
+                break;
             }
+            startlevel = 3 - sl0;
             break;
-        case 9: /* 4KB Pages.  */
-            if (level == 0 && outputsize <= 42) {
-                return false;
+        case 13: /* 64KB */
+            switch (sl0) {
+            case 2:
+                if (arm_pamax(cpu) < 44) {
+                    goto fail;
+                }
+                break;
+            case 3:
+                goto fail;
             }
+            startlevel = 3 - sl0;
             break;
         default:
             g_assert_not_reached();
         }
-
-        /* Inputsize checks.  */
-        if (inputsize > outputsize &&
-            (arm_el_is_aa64(&cpu->env, 1) || inputsize > 40)) {
-            /* This is CONSTRAINED UNPREDICTABLE and we choose to fault.  */
-            return false;
-        }
     } else {
-        /* AArch32 only supports 4KB pages. Assert on that.  */
+        /*
+         * Things are simpler for AArch32 EL2, with only 4k pages.
+         * There is no separate S2InvalidSL function, but AArch32.S2Walk
+         * begins with walkparms.sl0 in {'1x'}.
+         */
         assert(stride == 9);
-
-        if (level == 0) {
-            return false;
+        if (sl0 >= 2) {
+            goto fail;
         }
+        startlevel = 2 - sl0;
     }
-    return true;
+
+    /* AArch{64,32}.S2InconsistentSL are functionally equivalent.  */
+    levels = 3 - startlevel;
+    granulebits = stride + 3;
+
+    s1_min_iasize = levels * stride + granulebits + 1;
+    s1_max_iasize = s1_min_iasize + (stride - 1) + 4;
+
+    if (iasize >= s1_min_iasize && iasize <= s1_max_iasize) {
+        return startlevel;
+    }
+
+ fail:
+    return INT_MIN;
 }
 
 /**
@@ -1296,38 +1345,10 @@ static bool get_phys_addr_lpae(CPUARMState *env, S1Translate *ptw,
          */
         level = 4 - (inputsize - 4) / stride;
     } else {
-        /*
-         * For stage 2 translations the starting level is specified by the
-         * VTCR_EL2.SL0 field (whose interpretation depends on the page size)
-         */
-        uint32_t sl0 = extract32(tcr, 6, 2);
-        uint32_t sl2 = extract64(tcr, 33, 1);
-        int32_t startlevel;
-        bool ok;
-
-        /* SL2 is RES0 unless DS=1 & 4kb granule. */
-        if (param.ds && stride == 9 && sl2) {
-            if (sl0 != 0) {
-                level = 0;
-                goto do_translation_fault;
-            }
-            startlevel = -1;
-        } else if (!aarch64 || stride == 9) {
-            /* AArch32 or 4KB pages */
-            startlevel = 2 - sl0;
-
-            if (cpu_isar_feature(aa64_st, cpu)) {
-                startlevel &= 3;
-            }
-        } else {
-            /* 16KB or 64KB pages */
-            startlevel = 3 - sl0;
-        }
-
-        /* Check that the starting level is valid. */
-        ok = check_s2_mmu_setup(cpu, aarch64, startlevel,
-                                inputsize, stride, outputsize);
-        if (!ok) {
+        int startlevel = check_s2_mmu_setup(cpu, aarch64, tcr, param.ds,
+                                            inputsize, stride);
+        if (startlevel == INT_MIN) {
+            level = 0;
             goto do_translation_fault;
         }
         level = startlevel;
