target/arm: Support more GM blocksizes

Support all of the easy GM block sizes.
Use direct memory operations, since the pointers are aligned.

While BS=2 (16 bytes, 1 tag) is a legal setting, that requires
an atomic store of one nibble.  This is not difficult, but there
is also no point in supporting it until required.

Note that cortex-a710 sets GM blocksize to match its cacheline
size of 64 bytes.  I expect many implementations will also
match the cacheline, which makes 16 bytes very unlikely.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20230811214031.171020-4-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/cpu.c

@@ -2056,16 +2056,26 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
                                        ID_PFR1, VIRTUALIZATION, 0);
     }
 
+    if (cpu_isar_feature(aa64_mte, cpu)) {
+        /*
+         * The architectural range of GM blocksize is 2-6, however qemu
+         * doesn't support blocksize of 2 (see HELPER(ldgm)).
+         */
+        if (tcg_enabled()) {
+            assert(cpu->gm_blocksize >= 3 && cpu->gm_blocksize <= 6);
+        }
+
 #ifndef CONFIG_USER_ONLY
-    if (cpu->tag_memory == NULL && cpu_isar_feature(aa64_mte, cpu)) {
         /*
          * Disable the MTE feature bits if we do not have tag-memory
          * provided by the machine.
          */
-        cpu->isar.id_aa64pfr1 =
-            FIELD_DP64(cpu->isar.id_aa64pfr1, ID_AA64PFR1, MTE, 0);
-    }
+        if (cpu->tag_memory == NULL) {
+            cpu->isar.id_aa64pfr1 =
+                FIELD_DP64(cpu->isar.id_aa64pfr1, ID_AA64PFR1, MTE, 0);
+        }
 #endif
+    }
 
     if (tcg_enabled()) {
         /*

target/arm/tcg/mte_helper.c

@@ -428,6 +428,8 @@ uint64_t HELPER(ldgm)(CPUARMState *env, uint64_t ptr)
     int gm_bs = env_archcpu(env)->gm_blocksize;
     int gm_bs_bytes = 4 << gm_bs;
     void *tag_mem;
+    uint64_t ret;
+    int shift;
 
     ptr = QEMU_ALIGN_DOWN(ptr, gm_bs_bytes);
 
@@ -443,16 +445,41 @@ uint64_t HELPER(ldgm)(CPUARMState *env, uint64_t ptr)
 
     /*
      * The ordering of elements within the word corresponds to
-     * a little-endian operation.
+     * a little-endian operation.  Computation of shift comes from
+     *
+     *     index = address<LOG2_TAG_GRANULE+3:LOG2_TAG_GRANULE>
+     *     data<index*4+3:index*4> = tag
+     *
+     * Because of the alignment of ptr above, BS=6 has shift=0.
+     * All memory operations are aligned.  Defer support for BS=2,
+     * requiring insertion or extraction of a nibble, until we
+     * support a cpu that requires it.
      */
     switch (gm_bs) {
+    case 3:
+        /* 32 bytes -> 2 tags -> 8 result bits */
+        ret = *(uint8_t *)tag_mem;
+        break;
+    case 4:
+        /* 64 bytes -> 4 tags -> 16 result bits */
+        ret = cpu_to_le16(*(uint16_t *)tag_mem);
+        break;
+    case 5:
+        /* 128 bytes -> 8 tags -> 32 result bits */
+        ret = cpu_to_le32(*(uint32_t *)tag_mem);
+        break;
     case 6:
         /* 256 bytes -> 16 tags -> 64 result bits */
-        return ldq_le_p(tag_mem);
+        return cpu_to_le64(*(uint64_t *)tag_mem);
     default:
-        /* cpu configured with unsupported gm blocksize. */
+        /*
+         * CPU configured with unsupported/invalid gm blocksize.
+         * This is detected early in arm_cpu_realizefn.
+         */
         g_assert_not_reached();
     }
+    shift = extract64(ptr, LOG2_TAG_GRANULE, 4) * 4;
+    return ret << shift;
 }
 
 void HELPER(stgm)(CPUARMState *env, uint64_t ptr, uint64_t val)
@@ -462,6 +489,7 @@ void HELPER(stgm)(CPUARMState *env, uint64_t ptr, uint64_t val)
     int gm_bs = env_archcpu(env)->gm_blocksize;
     int gm_bs_bytes = 4 << gm_bs;
     void *tag_mem;
+    int shift;
 
     ptr = QEMU_ALIGN_DOWN(ptr, gm_bs_bytes);
 
@@ -478,13 +506,25 @@ void HELPER(stgm)(CPUARMState *env, uint64_t ptr, uint64_t val)
         return;
     }
 
-    /*
-     * The ordering of elements within the word corresponds to
-     * a little-endian operation.
-     */
+    /* See LDGM for comments on BS and on shift.  */
+    shift = extract64(ptr, LOG2_TAG_GRANULE, 4) * 4;
+    val >>= shift;
     switch (gm_bs) {
+    case 3:
+        /* 32 bytes -> 2 tags -> 8 result bits */
+        *(uint8_t *)tag_mem = val;
+        break;
+    case 4:
+        /* 64 bytes -> 4 tags -> 16 result bits */
+        *(uint16_t *)tag_mem = cpu_to_le16(val);
+        break;
+    case 5:
+        /* 128 bytes -> 8 tags -> 32 result bits */
+        *(uint32_t *)tag_mem = cpu_to_le32(val);
+        break;
     case 6:
-        stq_le_p(tag_mem, val);
+        /* 256 bytes -> 16 tags -> 64 result bits */
+        *(uint64_t *)tag_mem = cpu_to_le64(val);
         break;
     default:
         /* cpu configured with unsupported gm blocksize. */