arm: Implement HFNMIENA support for M profile MPU

Implement HFNMIENA support for the M profile MPU. This bit controls
whether the MPU is treated as enabled when executing at execution
priorities of less than zero (in NMI, HardFault or with the FAULTMASK
bit set).

Doing this requires us to use a different MMU index for "running
at execution priority < 0", because we will have different
access permissions for that case versus the normal case.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1493122030-32191-14-git-send-email-peter.maydell@linaro.org

1 files changed, 23 insertions, 1 deletions

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index 5c46c48889..13da5036bc 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -2045,6 +2045,18 @@ static inline bool arm_excp_unmasked(CPUState *cs, unsigned int excp_idx,
  * for the accesses done as part of a stage 1 page table walk, rather than
  * having to walk the stage 2 page table over and over.)
  *
+ * R profile CPUs have an MPU, but can use the same set of MMU indexes
+ * as A profile. They only need to distinguish NS EL0 and NS EL1 (and
+ * NS EL2 if we ever model a Cortex-R52).
+ *
+ * M profile CPUs are rather different as they do not have a true MMU.
+ * They have the following different MMU indexes:
+ *  User
+ *  Privileged
+ *  Execution priority negative (this is like privileged, but the
+ *  MPU HFNMIENA bit means that it may have different access permission
+ *  check results to normal privileged code, so can't share a TLB).
+ *
  * The ARMMMUIdx and the mmu index value used by the core QEMU TLB code
  * are not quite the same -- different CPU types (most notably M profile
  * vs A/R profile) would like to use MMU indexes with different semantics,
@@ -2080,6 +2092,7 @@ typedef enum ARMMMUIdx {
     ARMMMUIdx_S2NS = 6 | ARM_MMU_IDX_A,
     ARMMMUIdx_MUser = 0 | ARM_MMU_IDX_M,
     ARMMMUIdx_MPriv = 1 | ARM_MMU_IDX_M,
+    ARMMMUIdx_MNegPri = 2 | ARM_MMU_IDX_M,
     /* Indexes below here don't have TLBs and are used only for AT system
      * instructions or for the first stage of an S12 page table walk.
      */
@@ -2100,6 +2113,7 @@ typedef enum ARMMMUIdxBit {
     ARMMMUIdxBit_S2NS = 1 << 6,
     ARMMMUIdxBit_MUser = 1 << 0,
     ARMMMUIdxBit_MPriv = 1 << 1,
+    ARMMMUIdxBit_MNegPri = 1 << 2,
 } ARMMMUIdxBit;
 
 #define MMU_USER_IDX 0
@@ -2125,7 +2139,7 @@ static inline int arm_mmu_idx_to_el(ARMMMUIdx mmu_idx)
     case ARM_MMU_IDX_A:
         return mmu_idx & 3;
     case ARM_MMU_IDX_M:
-        return mmu_idx & 1;
+        return mmu_idx == ARMMMUIdx_MUser ? 0 : 1;
     default:
         g_assert_not_reached();
     }
@@ -2139,6 +2153,14 @@ static inline int cpu_mmu_index(CPUARMState *env, bool ifetch)
     if (arm_feature(env, ARM_FEATURE_M)) {
         ARMMMUIdx mmu_idx = el == 0 ? ARMMMUIdx_MUser : ARMMMUIdx_MPriv;
 
+        /* Execution priority is negative if FAULTMASK is set or
+         * we're in a HardFault or NMI handler.
+         */
+        if ((env->v7m.exception > 0 && env->v7m.exception <= 3)
+            || env->daif & PSTATE_F) {
+            return arm_to_core_mmu_idx(ARMMMUIdx_MNegPri);
+        }
+
         return arm_to_core_mmu_idx(mmu_idx);
     }