[PULL 018/119] target/arm: Disable FEAT_F64MM if maximum SVE vector size too small

[Peter Maydell]

From: Richard Henderson <richard.hender...@linaro.org>

All F64MM instructions operate on a 256-bit vector.
If only 128-bit vectors is supported by the cpu,
then the cpu cannot enable F64MM.

Suggested-by: Peter Maydell <peter.mayd...@linaro.org>
Reviewed-by: Peter Maydell <peter.mayd...@linaro.org>
Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
Message-id: 20250704142112.1018902-7-richard.hender...@linaro.org
Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
---
 target/arm/cpu64.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index 1f3406708bd..77e7c4a6a52 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -259,6 +259,13 @@ void arm_cpu_sve_finalize(ARMCPU *cpu, Error **errp)
     /* From now on sve_max_vq is the actual maximum supported length. */
     cpu->sve_max_vq = max_vq;
     cpu->sve_vq.map = vq_map;
+
+    /* FEAT_F64MM requires the existence of a 256-bit vector size. */
+    if (max_vq < 2) {
+        uint64_t t = GET_IDREG(&cpu->isar, ID_AA64ZFR0);
+        t = FIELD_DP64(t, ID_AA64ZFR0, F64MM, 0);
+        SET_IDREG(&cpu->isar, ID_AA64ZFR0, t);
+    }
 }
 
 /*
-- 
2.43.0