target/arm: Enable FEAT_CSV2_2 for -cpu max

There is no branch prediction in TCG, therefore there is no
need to actually include the context number into the predictor.
Therefore all we need to do is add the state for SCXTNUM_ELx.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220506180242.216785-21-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

docs/system/arm/emulation.rst

@@ -13,6 +13,9 @@ the following architecture extensions:
 - FEAT_BF16 (AArch64 BFloat16 instructions)
 - FEAT_BTI (Branch Target Identification)
 - FEAT_CSV2 (Cache speculation variant 2)
+- 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_DIT (Data Independent Timing instructions)
 - FEAT_DPB (DC CVAP instruction)
 - FEAT_Debugv8p2 (Debug changes for v8.2)

target/arm/cpu.c

@@ -230,6 +230,11 @@ static void arm_cpu_reset(DeviceState *dev)
              */
             env->cp15.gcr_el1 = 0x1ffff;
         }
+        /*
+         * Disable access to SCXTNUM_EL0 from CSV2_1p2.
+         * This is not yet exposed from the Linux kernel in any way.
+         */
+        env->cp15.sctlr_el[1] |= SCTLR_TSCXT;
 #else
         /* Reset into the highest available EL */
         if (arm_feature(env, ARM_FEATURE_EL3)) {

target/arm/cpu.h

@@ -688,6 +688,8 @@ typedef struct CPUArchState {
         ARMPACKey apdb;
         ARMPACKey apga;
     } keys;
+
+    uint64_t scxtnum_el[4];
 #endif
 
 #if defined(CONFIG_USER_ONLY)
@@ -1211,6 +1213,7 @@ void pmu_init(ARMCPU *cpu);
 #define SCTLR_WXN     (1U << 19)
 #define SCTLR_ST      (1U << 20) /* up to ??, RAZ in v6 */
 #define SCTLR_UWXN    (1U << 20) /* v7 onward, AArch32 only */
+#define SCTLR_TSCXT   (1U << 20) /* FEAT_CSV2_1p2, AArch64 only */
 #define SCTLR_FI      (1U << 21) /* up to v7, v8 RES0 */
 #define SCTLR_IESB    (1U << 21) /* v8.2-IESB, AArch64 only */
 #define SCTLR_U       (1U << 22) /* up to v6, RAO in v7 */
@@ -4022,6 +4025,19 @@ static inline bool isar_feature_aa64_dit(const ARMISARegisters *id)
     return FIELD_EX64(id->id_aa64pfr0, ID_AA64PFR0, DIT) != 0;
 }
 
+static inline bool isar_feature_aa64_scxtnum(const ARMISARegisters *id)
+{
+    int key = FIELD_EX64(id->id_aa64pfr0, ID_AA64PFR0, CSV2);
+    if (key >= 2) {
+        return true;      /* FEAT_CSV2_2 */
+    }
+    if (key == 1) {
+        key = FIELD_EX64(id->id_aa64pfr1, ID_AA64PFR1, CSV2_FRAC);
+        return key >= 2;  /* FEAT_CSV2_1p2 */
+    }
+    return false;
+}
+
 static inline bool isar_feature_aa64_ssbs(const ARMISARegisters *id)
 {
     return FIELD_EX64(id->id_aa64pfr1, ID_AA64PFR1, SSBS) != 0;

target/arm/cpu64.c

@@ -748,7 +748,7 @@ static void aarch64_max_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, 1);      /* FEAT_CSV2 */
+    t = FIELD_DP64(t, ID_AA64PFR0, CSV2, 2);      /* FEAT_CSV2_2 */
     cpu->isar.id_aa64pfr0 = t;
 
     t = cpu->isar.id_aa64pfr1;
@@ -760,6 +760,7 @@ static void aarch64_max_initfn(Object *obj)
      * we do for EL2 with the virtualization=on property.
      */
     t = FIELD_DP64(t, ID_AA64PFR1, MTE, 3);       /* FEAT_MTE3 */
+    t = FIELD_DP64(t, ID_AA64PFR1, CSV2_FRAC, 0); /* FEAT_CSV2_2 */
     cpu->isar.id_aa64pfr1 = t;
 
     t = cpu->isar.id_aa64mmfr0;

target/arm/helper.c

@@ -1770,6 +1770,9 @@ static void scr_write(CPUARMState *env, const ARMCPRegInfo *ri, uint64_t value)
         if (cpu_isar_feature(aa64_mte, cpu)) {
             valid_mask |= SCR_ATA;
         }
+        if (cpu_isar_feature(aa64_scxtnum, cpu)) {
+            valid_mask |= SCR_ENSCXT;
+        }
     } else {
         valid_mask &= ~(SCR_RW | SCR_ST);
         if (cpu_isar_feature(aa32_ras, cpu)) {
@@ -5149,6 +5152,9 @@ static void do_hcr_write(CPUARMState *env, uint64_t value, uint64_t valid_mask)
         if (cpu_isar_feature(aa64_mte, cpu)) {
             valid_mask |= HCR_ATA | HCR_DCT | HCR_TID5;
         }
+        if (cpu_isar_feature(aa64_scxtnum, cpu)) {
+            valid_mask |= HCR_ENSCXT;
+        }
     }
 
     /* Clear RES0 bits.  */
@@ -5800,6 +5806,10 @@ static void define_arm_vh_e2h_redirects_aliases(ARMCPU *cpu)
         { K(3, 0,  5, 6, 0), K(3, 4,  5, 6, 0), K(3, 5, 5, 6, 0),
           "TFSR_EL1", "TFSR_EL2", "TFSR_EL12", isar_feature_aa64_mte },
 
+        { K(3, 0, 13, 0, 7), K(3, 4, 13, 0, 7), K(3, 5, 13, 0, 7),
+          "SCXTNUM_EL1", "SCXTNUM_EL2", "SCXTNUM_EL12",
+          isar_feature_aa64_scxtnum },
+
         /* TODO: ARMv8.2-SPE -- PMSCR_EL2 */
         /* TODO: ARMv8.4-Trace -- TRFCR_EL2 */
     };
@@ -7223,7 +7233,52 @@ static const ARMCPRegInfo mte_el0_cacheop_reginfo[] = {
     },
 };
 
-#endif
+static CPAccessResult access_scxtnum(CPUARMState *env, const ARMCPRegInfo *ri,
+                                     bool isread)
+{
+    uint64_t hcr = arm_hcr_el2_eff(env);
+    int el = arm_current_el(env);
+
+    if (el == 0 && !((hcr & HCR_E2H) && (hcr & HCR_TGE))) {
+        if (env->cp15.sctlr_el[1] & SCTLR_TSCXT) {
+            if (hcr & HCR_TGE) {
+                return CP_ACCESS_TRAP_EL2;
+            }
+            return CP_ACCESS_TRAP;
+        }
+    } else if (el < 2 && (env->cp15.sctlr_el[2] & SCTLR_TSCXT)) {
+        return CP_ACCESS_TRAP_EL2;
+    }
+    if (el < 2 && arm_is_el2_enabled(env) && !(hcr & HCR_ENSCXT)) {
+        return CP_ACCESS_TRAP_EL2;
+    }
+    if (el < 3
+        && arm_feature(env, ARM_FEATURE_EL3)
+        && !(env->cp15.scr_el3 & SCR_ENSCXT)) {
+        return CP_ACCESS_TRAP_EL3;
+    }
+    return CP_ACCESS_OK;
+}
+
+static const ARMCPRegInfo scxtnum_reginfo[] = {
+    { .name = "SCXTNUM_EL0", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 3, .crn = 13, .crm = 0, .opc2 = 7,
+      .access = PL0_RW, .accessfn = access_scxtnum,
+      .fieldoffset = offsetof(CPUARMState, scxtnum_el[0]) },
+    { .name = "SCXTNUM_EL1", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 0, .crn = 13, .crm = 0, .opc2 = 7,
+      .access = PL1_RW, .accessfn = access_scxtnum,
+      .fieldoffset = offsetof(CPUARMState, scxtnum_el[1]) },
+    { .name = "SCXTNUM_EL2", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 4, .crn = 13, .crm = 0, .opc2 = 7,
+      .access = PL2_RW, .accessfn = access_scxtnum,
+      .fieldoffset = offsetof(CPUARMState, scxtnum_el[2]) },
+    { .name = "SCXTNUM_EL3", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 6, .crn = 13, .crm = 0, .opc2 = 7,
+      .access = PL3_RW,
+      .fieldoffset = offsetof(CPUARMState, scxtnum_el[3]) },
+};
+#endif /* TARGET_AARCH64 */
 
 static CPAccessResult access_predinv(CPUARMState *env, const ARMCPRegInfo *ri,
                                      bool isread)
@@ -8365,6 +8420,10 @@ void register_cp_regs_for_features(ARMCPU *cpu)
         define_arm_cp_regs(cpu, mte_tco_ro_reginfo);
         define_arm_cp_regs(cpu, mte_el0_cacheop_reginfo);
     }
+
+    if (cpu_isar_feature(aa64_scxtnum, cpu)) {
+        define_arm_cp_regs(cpu, scxtnum_reginfo);
+    }
 #endif
 
     if (cpu_isar_feature(any_predinv, cpu)) {