target/arm: Enable FEAT_CSV2_3 for -cpu max

FEAT_CSV2_3 adds a mechanism to identify if hardware cannot disclose
information about whether branch targets and branch history trained
in one hardware described context can control speculative execution
in a different hardware context.

There is no branch prediction in TCG, so we don't need to do anything
to be compliant with this.  Upadte the '-cpu max' ID registers to
advertise the feature.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240418152004.2106516-3-peter.maydell@linaro.org

docs/system/arm/emulation.rst

@@ -32,6 +32,7 @@ the following architecture extensions:
 - FEAT_CSV2_1p1 (Cache speculation variant 2, version 1.1)
 - FEAT_CSV2_1p2 (Cache speculation variant 2, version 1.2)
 - FEAT_CSV2_2 (Cache speculation variant 2, version 2)
+- FEAT_CSV2_3 (Cache speculation variant 2, version 3)
 - FEAT_CSV3 (Cache speculation variant 3)
 - FEAT_DGH (Data gathering hint)
 - FEAT_DIT (Data Independent Timing instructions)

target/arm/tcg/cpu64.c

@@ -1159,7 +1159,7 @@ void aarch64_max_tcg_initfn(Object *obj)
     t = FIELD_DP64(t, ID_AA64PFR0, SVE, 1);
     t = FIELD_DP64(t, ID_AA64PFR0, SEL2, 1);      /* FEAT_SEL2 */
     t = FIELD_DP64(t, ID_AA64PFR0, DIT, 1);       /* FEAT_DIT */
-    t = FIELD_DP64(t, ID_AA64PFR0, CSV2, 2);      /* FEAT_CSV2_2 */
+    t = FIELD_DP64(t, ID_AA64PFR0, CSV2, 3);      /* FEAT_CSV2_3 */
     t = FIELD_DP64(t, ID_AA64PFR0, CSV3, 1);      /* FEAT_CSV3 */
     cpu->isar.id_aa64pfr0 = t;
 
@@ -1174,7 +1174,7 @@ void aarch64_max_tcg_initfn(Object *obj)
     t = FIELD_DP64(t, ID_AA64PFR1, MTE, 3);       /* FEAT_MTE3 */
     t = FIELD_DP64(t, ID_AA64PFR1, RAS_FRAC, 0);  /* FEAT_RASv1p1 + FEAT_DoubleFault */
     t = FIELD_DP64(t, ID_AA64PFR1, SME, 1);       /* FEAT_SME */
-    t = FIELD_DP64(t, ID_AA64PFR1, CSV2_FRAC, 0); /* FEAT_CSV2_2 */
+    t = FIELD_DP64(t, ID_AA64PFR1, CSV2_FRAC, 0); /* FEAT_CSV2_3 */
     t = FIELD_DP64(t, ID_AA64PFR1, NMI, 1);       /* FEAT_NMI */
     cpu->isar.id_aa64pfr1 = t;