target/arm/ptw: Check for block descriptors at invalid levels

The architecture doesn't permit block descriptors at any arbitrary
level of the page table walk; it depends on the granule size which
levels are permitted.  We implemented only a partial version of this
check which assumes that block descriptors are valid at all levels
except level 3, which meant that we wouldn't deliver the Translation
fault for all cases of this sort of guest page table error.

Implement the logic corresponding to the pseudocode
AArch64.DecodeDescriptorType() and AArch64.BlockDescSupported().

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230807141514.19075-14-peter.maydell@linaro.org

target/arm/ptw.c

@@ -1551,6 +1551,25 @@ static int check_s2_mmu_setup(ARMCPU *cpu, bool is_aa64, uint64_t tcr,
     return INT_MIN;
 }
 
+static bool lpae_block_desc_valid(ARMCPU *cpu, bool ds,
+                                  ARMGranuleSize gran, int level)
+{
+    /*
+     * See pseudocode AArch46.BlockDescSupported(): block descriptors
+     * are not valid at all levels, depending on the page size.
+     */
+    switch (gran) {
+    case Gran4K:
+        return (level == 0 && ds) || level == 1 || level == 2;
+    case Gran16K:
+        return (level == 1 && ds) || level == 2;
+    case Gran64K:
+        return (level == 1 && arm_pamax(cpu) == 52) || level == 2;
+    default:
+        g_assert_not_reached();
+    }
+}
+
 /**
  * get_phys_addr_lpae: perform one stage of page table walk, LPAE format
  *
@@ -1786,8 +1805,10 @@ static bool get_phys_addr_lpae(CPUARMState *env, S1Translate *ptw,
     new_descriptor = descriptor;
 
  restart_atomic_update:
-    if (!(descriptor & 1) || (!(descriptor & 2) && (level == 3))) {
-        /* Invalid, or the Reserved level 3 encoding */
+    if (!(descriptor & 1) ||
+        (!(descriptor & 2) &&
+         !lpae_block_desc_valid(cpu, param.ds, param.gran, level))) {
+        /* Invalid, or a block descriptor at an invalid level */
         goto do_translation_fault;
     }