target/arm: Adjust and validate mtedesc sizem1

When we added SVE_MTEDESC_SHIFT, we effectively limited the
maximum size of MTEDESC.  Adjust SIZEM1 to consume the remaining
bits (32 - 10 - 5 - 12 == 5).  Assert that the data to be stored
fits within the field (expecting 8 * 4 - 1 == 31, exact fit).

Cc: qemu-stable@nongnu.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Gustavo Romero <gustavo.romero@linaro.org>
Message-id: 20240207025210.8837-4-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
(cherry picked from commit b12a767)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

target/arm/internals.h

@@ -1273,7 +1273,7 @@ FIELD(MTEDESC, TBI,   4, 2)
 FIELD(MTEDESC, TCMA,  6, 2)
 FIELD(MTEDESC, WRITE, 8, 1)
 FIELD(MTEDESC, ALIGN, 9, 3)
-FIELD(MTEDESC, SIZEM1, 12, SIMD_DATA_BITS - 12)  /* size - 1 */
+FIELD(MTEDESC, SIZEM1, 12, SIMD_DATA_BITS - SVE_MTEDESC_SHIFT - 12)  /* size - 1 */
 
 bool mte_probe(CPUARMState *env, uint32_t desc, uint64_t ptr);
 uint64_t mte_check(CPUARMState *env, uint32_t desc, uint64_t ptr, uintptr_t ra);

target/arm/tcg/translate-sve.c

@@ -4443,17 +4443,18 @@ static void do_mem_zpa(DisasContext *s, int zt, int pg, TCGv_i64 addr,
 {
     unsigned vsz = vec_full_reg_size(s);
     TCGv_ptr t_pg;
+    uint32_t sizem1;
     int desc = 0;
 
     assert(mte_n >= 1 && mte_n <= 4);
+    sizem1 = (mte_n << dtype_msz(dtype)) - 1;
+    assert(sizem1 <= R_MTEDESC_SIZEM1_MASK >> R_MTEDESC_SIZEM1_SHIFT);
     if (s->mte_active[0]) {
-        int msz = dtype_msz(dtype);
-
         desc = FIELD_DP32(desc, MTEDESC, MIDX, get_mem_index(s));
         desc = FIELD_DP32(desc, MTEDESC, TBI, s->tbid);
         desc = FIELD_DP32(desc, MTEDESC, TCMA, s->tcma);
         desc = FIELD_DP32(desc, MTEDESC, WRITE, is_write);
-        desc = FIELD_DP32(desc, MTEDESC, SIZEM1, (mte_n << msz) - 1);
+        desc = FIELD_DP32(desc, MTEDESC, SIZEM1, sizem1);
         desc <<= SVE_MTEDESC_SHIFT;
     } else {
         addr = clean_data_tbi(s, addr);