[PATCH] target/arm: Don't implement *32_EL2 registers when EL1 is AArch64 only

[PATCH] target/arm: Don't implement *32_EL2 registers when EL1 is AArch64 only

[Peter Maydell]

The system registers DBGVCR32_EL2, FPEXC32_EL2, DACR32_EL2 and
IFSR32_EL2 are present only to allow an AArch64 EL2 or EL3 to read
and write the contents of an AArch32-only system register.  The
architecture requires that they are present only when EL1 can be
AArch32, but we implement them unconditionally.  This was OK when all
our CPUs supported AArch32 EL1, but we have quite a lot of CPU models
now which only support AArch64 at EL1:
 a64fx
 cortex-a76
 cortex-a710
 neoverse-n1
 neoverse-n2
 neoverse-v1

Only define these registers for CPUs which allow AArch32 EL1.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
I happened to notice this reading through the Arm ARM recently.  This
is technically a bug, but you'll only notice it if you deliberately
look at what should be an unimplemented register to see if it UNDEFs,
so I don't think it's worth either putting in 8.2 or backporting to
stable.
---
 target/arm/debug_helper.c | 23 +++++++++++++++--------
 target/arm/helper.c       | 35 +++++++++++++++++++++--------------
 2 files changed, 36 insertions(+), 22 deletions(-)

diff --git a/target/arm/debug_helper.c b/target/arm/debug_helper.c
index cbfba532f50..83d2619080f 100644
--- a/target/arm/debug_helper.c
+++ b/target/arm/debug_helper.c
@@ -1026,14 +1026,6 @@ static const ARMCPRegInfo debug_cp_reginfo[] = {
       .cp = 14, .opc1 = 0, .crn = 0, .crm = 7, .opc2 = 0,
       .access = PL1_RW, .accessfn = access_tda,
       .type = ARM_CP_NOP },
-    /*
-     * Dummy DBGVCR32_EL2 (which is only for a 64-bit hypervisor
-     * to save and restore a 32-bit guest's DBGVCR)
-     */
-    { .name = "DBGVCR32_EL2", .state = ARM_CP_STATE_AA64,
-      .opc0 = 2, .opc1 = 4, .crn = 0, .crm = 7, .opc2 = 0,
-      .access = PL2_RW, .accessfn = access_tda,
-      .type = ARM_CP_NOP | ARM_CP_EL3_NO_EL2_KEEP },
     /*
      * Dummy MDCCINT_EL1, since we don't implement the Debug Communications
      * Channel but Linux may try to access this register. The 32-bit
@@ -1062,6 +1054,18 @@ static const ARMCPRegInfo debug_cp_reginfo[] = {
       .fieldoffset = offsetof(CPUARMState, cp15.dbgclaim) },
 };
 
+/* These are present only when EL1 supports AArch32 */
+static const ARMCPRegInfo debug_aa32_el1_reginfo[] = {
+    /*
+     * Dummy DBGVCR32_EL2 (which is only for a 64-bit hypervisor
+     * to save and restore a 32-bit guest's DBGVCR)
+     */
+    { .name = "DBGVCR32_EL2", .state = ARM_CP_STATE_AA64,
+      .opc0 = 2, .opc1 = 4, .crn = 0, .crm = 7, .opc2 = 0,
+      .access = PL2_RW, .accessfn = access_tda,
+      .type = ARM_CP_NOP | ARM_CP_EL3_NO_EL2_KEEP },
+};
+
 static const ARMCPRegInfo debug_lpae_cp_reginfo[] = {
     /* 64 bit access versions of the (dummy) debug registers */
     { .name = "DBGDRAR", .cp = 14, .crm = 1, .opc1 = 0,
@@ -1207,6 +1211,9 @@ void define_debug_regs(ARMCPU *cpu)
     assert(ctx_cmps <= brps);
 
     define_arm_cp_regs(cpu, debug_cp_reginfo);
+    if (cpu_isar_feature(aa64_aa32_el1, cpu)) {
+        define_arm_cp_regs(cpu, debug_aa32_el1_reginfo);
+    }
 
     if (arm_feature(&cpu->env, ARM_FEATURE_LPAE)) {
         define_arm_cp_regs(cpu, debug_lpae_cp_reginfo);
diff --git a/target/arm/helper.c b/target/arm/helper.c
index ff1970981ee..bf26b995171 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -5681,20 +5681,6 @@ static const ARMCPRegInfo v8_cp_reginfo[] = {
       .opc0 = 3, .opc1 = 0, .crn = 4, .crm = 2, .opc2 = 0,
       .type = ARM_CP_NO_RAW,
       .access = PL1_RW, .readfn = spsel_read, .writefn = spsel_write },
-    { .name = "FPEXC32_EL2", .state = ARM_CP_STATE_AA64,
-      .opc0 = 3, .opc1 = 4, .crn = 5, .crm = 3, .opc2 = 0,
-      .access = PL2_RW,
-      .type = ARM_CP_ALIAS | ARM_CP_FPU | ARM_CP_EL3_NO_EL2_KEEP,
-      .fieldoffset = offsetof(CPUARMState, vfp.xregs[ARM_VFP_FPEXC]) },
-    { .name = "DACR32_EL2", .state = ARM_CP_STATE_AA64,
-      .opc0 = 3, .opc1 = 4, .crn = 3, .crm = 0, .opc2 = 0,
-      .access = PL2_RW, .resetvalue = 0, .type = ARM_CP_EL3_NO_EL2_KEEP,
-      .writefn = dacr_write, .raw_writefn = raw_write,
-      .fieldoffset = offsetof(CPUARMState, cp15.dacr32_el2) },
-    { .name = "IFSR32_EL2", .state = ARM_CP_STATE_AA64,
-      .opc0 = 3, .opc1 = 4, .crn = 5, .crm = 0, .opc2 = 1,
-      .access = PL2_RW, .resetvalue = 0, .type = ARM_CP_EL3_NO_EL2_KEEP,
-      .fieldoffset = offsetof(CPUARMState, cp15.ifsr32_el2) },
     { .name = "SPSR_IRQ", .state = ARM_CP_STATE_AA64,
       .type = ARM_CP_ALIAS,
       .opc0 = 3, .opc1 = 4, .crn = 4, .crm = 3, .opc2 = 0,
@@ -5729,6 +5715,24 @@ static const ARMCPRegInfo v8_cp_reginfo[] = {
       .fieldoffset = offsetoflow32(CPUARMState, cp15.mdcr_el3) },
 };
 
+/* These are present only when EL1 supports AArch32 */
+static const ARMCPRegInfo v8_aa32_el1_reginfo[] = {
+    { .name = "FPEXC32_EL2", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 4, .crn = 5, .crm = 3, .opc2 = 0,
+      .access = PL2_RW,
+      .type = ARM_CP_ALIAS | ARM_CP_FPU | ARM_CP_EL3_NO_EL2_KEEP,
+      .fieldoffset = offsetof(CPUARMState, vfp.xregs[ARM_VFP_FPEXC]) },
+    { .name = "DACR32_EL2", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 4, .crn = 3, .crm = 0, .opc2 = 0,
+      .access = PL2_RW, .resetvalue = 0, .type = ARM_CP_EL3_NO_EL2_KEEP,
+      .writefn = dacr_write, .raw_writefn = raw_write,
+      .fieldoffset = offsetof(CPUARMState, cp15.dacr32_el2) },
+    { .name = "IFSR32_EL2", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 4, .crn = 5, .crm = 0, .opc2 = 1,
+      .access = PL2_RW, .resetvalue = 0, .type = ARM_CP_EL3_NO_EL2_KEEP,
+      .fieldoffset = offsetof(CPUARMState, cp15.ifsr32_el2) },
+};
+
 static void do_hcr_write(CPUARMState *env, uint64_t value, uint64_t valid_mask)
 {
     ARMCPU *cpu = env_archcpu(env);
@@ -8699,6 +8703,9 @@ void register_cp_regs_for_features(ARMCPU *cpu)
         }
         define_arm_cp_regs(cpu, v8_idregs);
         define_arm_cp_regs(cpu, v8_cp_reginfo);
+        if (cpu_isar_feature(aa64_aa32_el1, cpu)) {
+            define_arm_cp_regs(cpu, v8_aa32_el1_reginfo);
+        }
 
         for (i = 4; i < 16; i++) {
             /*
-- 
2.34.1

Re: [PATCH] target/arm: Don't implement *32_EL2 registers when EL1 is AArch64 only

[Richard Henderson]

On 11/21/23 08:46, Peter Maydell wrote:
> The system registers DBGVCR32_EL2, FPEXC32_EL2, DACR32_EL2 and
> IFSR32_EL2 are present only to allow an AArch64 EL2 or EL3 to read
> and write the contents of an AArch32-only system register.  The
> architecture requires that they are present only when EL1 can be
> AArch32, but we implement them unconditionally.  This was OK when all
> our CPUs supported AArch32 EL1, but we have quite a lot of CPU models
> now which only support AArch64 at EL1:
>   a64fx
>   cortex-a76
>   cortex-a710
>   neoverse-n1
>   neoverse-n2
>   neoverse-v1
> 
> Only define these registers for CPUs which allow AArch32 EL1.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> I happened to notice this reading through the Arm ARM recently.  This
> is technically a bug, but you'll only notice it if you deliberately
> look at what should be an unimplemented register to see if it UNDEFs,
> so I don't think it's worth either putting in 8.2 or backporting to
> stable.
> ---
>   target/arm/debug_helper.c | 23 +++++++++++++++--------
>   target/arm/helper.c       | 35 +++++++++++++++++++++--------------
>   2 files changed, 36 insertions(+), 22 deletions(-)

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


r~