target/arm: Implement v8M MSPLIM and PSPLIM registers

The v8M architecture includes hardware support for enforcing
stack pointer limits. We don't implement this behaviour yet,
but provide the MSPLIM and PSPLIM stack pointer limit registers
as reads-as-written, so that when we do implement the checks
in future this won't break guest migration.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180209165810.6668-12-peter.maydell@linaro.org

target/arm/cpu.h

@@ -498,6 +498,8 @@ typedef struct CPUARMState {
         uint32_t secure; /* Is CPU in Secure state? (not guest visible) */
         uint32_t csselr[M_REG_NUM_BANKS];
         uint32_t scr[M_REG_NUM_BANKS];
+        uint32_t msplim[M_REG_NUM_BANKS];
+        uint32_t psplim[M_REG_NUM_BANKS];
     } v7m;
 
     /* Information associated with an exception about to be taken:

target/arm/helper.c

@@ -10403,6 +10403,16 @@ uint32_t HELPER(v7m_mrs)(CPUARMState *env, uint32_t reg)
                 return 0;
             }
             return env->v7m.other_ss_psp;
+        case 0x8a: /* MSPLIM_NS */
+            if (!env->v7m.secure) {
+                return 0;
+            }
+            return env->v7m.msplim[M_REG_NS];
+        case 0x8b: /* PSPLIM_NS */
+            if (!env->v7m.secure) {
+                return 0;
+            }
+            return env->v7m.psplim[M_REG_NS];
         case 0x90: /* PRIMASK_NS */
             if (!env->v7m.secure) {
                 return 0;
@@ -10444,6 +10454,16 @@ uint32_t HELPER(v7m_mrs)(CPUARMState *env, uint32_t reg)
         return v7m_using_psp(env) ? env->v7m.other_sp : env->regs[13];
     case 9: /* PSP */
         return v7m_using_psp(env) ? env->regs[13] : env->v7m.other_sp;
+    case 10: /* MSPLIM */
+        if (!arm_feature(env, ARM_FEATURE_V8)) {
+            goto bad_reg;
+        }
+        return env->v7m.msplim[env->v7m.secure];
+    case 11: /* PSPLIM */
+        if (!arm_feature(env, ARM_FEATURE_V8)) {
+            goto bad_reg;
+        }
+        return env->v7m.psplim[env->v7m.secure];
     case 16: /* PRIMASK */
         return env->v7m.primask[env->v7m.secure];
     case 17: /* BASEPRI */
@@ -10452,6 +10472,7 @@ uint32_t HELPER(v7m_mrs)(CPUARMState *env, uint32_t reg)
     case 19: /* FAULTMASK */
         return env->v7m.faultmask[env->v7m.secure];
     default:
+    bad_reg:
         qemu_log_mask(LOG_GUEST_ERROR, "Attempt to read unknown special"
                                        " register %d\n", reg);
         return 0;
@@ -10489,6 +10510,18 @@ void HELPER(v7m_msr)(CPUARMState *env, uint32_t maskreg, uint32_t val)
             }
             env->v7m.other_ss_psp = val;
             return;
+        case 0x8a: /* MSPLIM_NS */
+            if (!env->v7m.secure) {
+                return;
+            }
+            env->v7m.msplim[M_REG_NS] = val & ~7;
+            return;
+        case 0x8b: /* PSPLIM_NS */
+            if (!env->v7m.secure) {
+                return;
+            }
+            env->v7m.psplim[M_REG_NS] = val & ~7;
+            return;
         case 0x90: /* PRIMASK_NS */
             if (!env->v7m.secure) {
                 return;
@@ -10568,6 +10601,18 @@ void HELPER(v7m_msr)(CPUARMState *env, uint32_t maskreg, uint32_t val)
             env->v7m.other_sp = val;
         }
         break;
+    case 10: /* MSPLIM */
+        if (!arm_feature(env, ARM_FEATURE_V8)) {
+            goto bad_reg;
+        }
+        env->v7m.msplim[env->v7m.secure] = val & ~7;
+        break;
+    case 11: /* PSPLIM */
+        if (!arm_feature(env, ARM_FEATURE_V8)) {
+            goto bad_reg;
+        }
+        env->v7m.psplim[env->v7m.secure] = val & ~7;
+        break;
     case 16: /* PRIMASK */
         env->v7m.primask[env->v7m.secure] = val & 1;
         break;
@@ -10600,6 +10645,7 @@ void HELPER(v7m_msr)(CPUARMState *env, uint32_t maskreg, uint32_t val)
         env->v7m.control[env->v7m.secure] |= val & R_V7M_CONTROL_NPRIV_MASK;
         break;
     default:
+    bad_reg:
         qemu_log_mask(LOG_GUEST_ERROR, "Attempt to write unknown special"
                                        " register %d\n", reg);
         return;

target/arm/machine.c

@@ -246,6 +246,26 @@ static const VMStateDescription vmstate_m_other_sp = {
     }
 };
 
+static bool m_v8m_needed(void *opaque)
+{
+    ARMCPU *cpu = opaque;
+    CPUARMState *env = &cpu->env;
+
+    return arm_feature(env, ARM_FEATURE_M) && arm_feature(env, ARM_FEATURE_V8);
+}
+
+static const VMStateDescription vmstate_m_v8m = {
+    .name = "cpu/m/v8m",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = m_v8m_needed,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32_ARRAY(env.v7m.msplim, ARMCPU, M_REG_NUM_BANKS),
+        VMSTATE_UINT32_ARRAY(env.v7m.psplim, ARMCPU, M_REG_NUM_BANKS),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static const VMStateDescription vmstate_m = {
     .name = "cpu/m",
     .version_id = 4,
@@ -270,6 +290,7 @@ static const VMStateDescription vmstate_m = {
         &vmstate_m_csselr,
         &vmstate_m_scr,
         &vmstate_m_other_sp,
+        &vmstate_m_v8m,
         NULL
     }
 };