For FEAT_ECV, new registers CNTPCTSS_EL0 and CNTVCTSS_EL0 are
defined, which are "self-synchronized" views of the physical and
virtual counts as seen in the CNTPCT_EL0 and CNTVCT_EL0 registers
(meaning that no barriers are needed around accesses to them to
ensure that reads of them do not occur speculatively and out-of-order
with other instructions).

For QEMU, all our system registers are self-synchronized, so we can
simply copy the existing implementation of CNTPCT_EL0 and CNTVCT_EL0
to the new register encodings.

This means we now implement all the functionality required for
ID_AA64MMFR0_EL1.ECV == 0b0001.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/helper.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/target/arm/helper.c b/target/arm/helper.c
index 6c528903a9a..3441b14ba39 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -3389,6 +3389,34 @@ static const ARMCPRegInfo generic_timer_cp_reginfo[] = {
     },
 };
 
+/*
+ * FEAT_ECV adds extra views of CNTVCT_EL0 and CNTPCT_EL0 which
+ * are "self-synchronizing". For QEMU all sysregs are self-synchronizing,
+ * so our implementations here are identical to the normal registers.
+ */
+static const ARMCPRegInfo gen_timer_ecv_cp_reginfo[] = {
+    { .name = "CNTVCTSS", .cp = 15, .crm = 14, .opc1 = 9,
+      .access = PL0_R, .type = ARM_CP_64BIT | ARM_CP_NO_RAW | ARM_CP_IO,
+      .accessfn = gt_vct_access,
+      .readfn = gt_virt_cnt_read, .resetfn = arm_cp_reset_ignore,
+    },
+    { .name = "CNTVCTSS_EL0", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 3, .crn = 14, .crm = 0, .opc2 = 6,
+      .access = PL0_R, .type = ARM_CP_NO_RAW | ARM_CP_IO,
+      .accessfn = gt_vct_access, .readfn = gt_virt_cnt_read,
+    },
+    { .name = "CNTPCTSS", .cp = 15, .crm = 14, .opc1 = 8,
+      .access = PL0_R, .type = ARM_CP_64BIT | ARM_CP_NO_RAW | ARM_CP_IO,
+      .accessfn = gt_pct_access,
+      .readfn = gt_cnt_read, .resetfn = arm_cp_reset_ignore,
+    },
+    { .name = "CNTPCTSS_EL0", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 3, .crn = 14, .crm = 0, .opc2 = 5,
+      .access = PL0_R, .type = ARM_CP_NO_RAW | ARM_CP_IO,
+      .accessfn = gt_pct_access, .readfn = gt_cnt_read,
+    },
+};
+
 #else
 
 /*
@@ -3422,6 +3450,18 @@ static const ARMCPRegInfo generic_timer_cp_reginfo[] = {
     },
 };
 
+/*
+ * CNTVCTSS_EL0 has the same trap conditions as CNTVCT_EL0, so it also
+ * is exposed to userspace by Linux.
+ */
+static const ARMCPRegInfo gen_timer_ecv_cp_reginfo[] = {
+    { .name = "CNTVCTSS_EL0", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 3, .crn = 14, .crm = 0, .opc2 = 6,
+      .access = PL0_R, .type = ARM_CP_NO_RAW | ARM_CP_IO,
+      .readfn = gt_virt_cnt_read,
+    },
+};
+
 #endif
 
 static void par_write(CPUARMState *env, const ARMCPRegInfo *ri, uint64_t value)
@@ -9258,6 +9298,9 @@ void register_cp_regs_for_features(ARMCPU *cpu)
     if (arm_feature(env, ARM_FEATURE_GENERIC_TIMER)) {
         define_arm_cp_regs(cpu, generic_timer_cp_reginfo);
     }
+    if (cpu_isar_feature(aa64_ecv_traps, cpu)) {
+        define_arm_cp_regs(cpu, gen_timer_ecv_cp_reginfo);
+    }
     if (arm_feature(env, ARM_FEATURE_VAPA)) {
         ARMCPRegInfo vapa_cp_reginfo[] = {
             { .name = "PAR", .cp = 15, .crn = 7, .crm = 4, .opc1 = 0, .opc2 = 0,
-- 
2.34.1

On 3/1/24 08:32, Peter Maydell wrote:
> For FEAT_ECV, new registers CNTPCTSS_EL0 and CNTVCTSS_EL0 are
> defined, which are "self-synchronized" views of the physical and
> virtual counts as seen in the CNTPCT_EL0 and CNTVCT_EL0 registers
> (meaning that no barriers are needed around accesses to them to
> ensure that reads of them do not occur speculatively and out-of-order
> with other instructions).
> 
> For QEMU, all our system registers are self-synchronized, so we can
> simply copy the existing implementation of CNTPCT_EL0 and CNTVCT_EL0
> to the new register encodings.
> 
> This means we now implement all the functionality required for
> ID_AA64MMFR0_EL1.ECV == 0b0001.
> 
> Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
> ---
>   target/arm/helper.c | 43 +++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 43 insertions(+)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~