target-arm: Implement SP_EL0, SP_EL1

Implement handling for the AArch64 SP_EL0 system register.
This holds the EL0 stack pointer, and is only accessible when
it's not being used as the stack pointer, ie when we're in EL1
and EL1 is using its own stack pointer. We also provide a
definition of the SP_EL1 register; this isn't guest visible
as a system register for an implementation like QEMU which
doesn't provide EL2 or EL3; however it is useful for ensuring
the underlying state is migrated.

We need to update the state fields in the CPU state whenever
we switch stack pointers; this happens when we take an exception
and also when SPSEL is used to change the bit in PSTATE which
indicates which stack pointer EL1 should use.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>

6 files changed, 100 insertions, 7 deletions

diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index ecdd7a73a6..28b9bda218 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -163,6 +163,7 @@ typedef struct CPUARMState {
     uint64_t daif; /* exception masks, in the bits they are in in PSTATE */
 
     uint64_t elr_el1; /* AArch64 ELR_EL1 */
+    uint64_t sp_el[2]; /* AArch64 banked stack pointers */
 
     /* System control coprocessor (cp15) */
     struct {
@@ -434,6 +435,7 @@ int arm_cpu_handle_mmu_fault(CPUState *cpu, vaddr address, int rw,
  * Only these are valid when in AArch64 mode; in
  * AArch32 mode SPSRs are basically CPSR-format.
  */
+#define PSTATE_SP (1U)
 #define PSTATE_M (0xFU)
 #define PSTATE_nRW (1U << 4)
 #define PSTATE_F (1U << 6)
diff --git a/target-arm/helper.c b/target-arm/helper.c
index 276ecf28dc..27a3dc2a75 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -1783,6 +1783,27 @@ static uint64_t aa64_dczid_read(CPUARMState *env, const ARMCPRegInfo *ri)
     return cpu->dcz_blocksize | dzp_bit;
 }
 
+static CPAccessResult sp_el0_access(CPUARMState *env, const ARMCPRegInfo *ri)
+{
+    if (!env->pstate & PSTATE_SP) {
+        /* Access to SP_EL0 is undefined if it's being used as
+         * the stack pointer.
+         */
+        return CP_ACCESS_TRAP_UNCATEGORIZED;
+    }
+    return CP_ACCESS_OK;
+}
+
+static uint64_t spsel_read(CPUARMState *env, const ARMCPRegInfo *ri)
+{
+    return env->pstate & PSTATE_SP;
+}
+
+static void spsel_write(CPUARMState *env, const ARMCPRegInfo *ri, uint64_t val)
+{
+    update_spsel(env, val);
+}
+
 static const ARMCPRegInfo v8_cp_reginfo[] = {
     /* Minimal set of EL0-visible registers. This will need to be expanded
      * significantly for system emulation of AArch64 CPUs.
@@ -1915,6 +1936,19 @@ static const ARMCPRegInfo v8_cp_reginfo[] = {
       .type = ARM_CP_NO_MIGRATE,
       .opc0 = 3, .opc1 = 0, .crn = 4, .crm = 0, .opc2 = 1,
       .access = PL1_RW, .fieldoffset = offsetof(CPUARMState, elr_el1) },
+    /* We rely on the access checks not allowing the guest to write to the
+     * state field when SPSel indicates that it's being used as the stack
+     * pointer.
+     */
+    { .name = "SP_EL0", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 0, .crn = 4, .crm = 1, .opc2 = 0,
+      .access = PL1_RW, .accessfn = sp_el0_access,
+      .type = ARM_CP_NO_MIGRATE,
+      .fieldoffset = offsetof(CPUARMState, sp_el[0]) },
+    { .name = "SPSel", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 0, .crn = 4, .crm = 2, .opc2 = 0,
+      .type = ARM_CP_NO_MIGRATE,
+      .access = PL1_RW, .readfn = spsel_read, .writefn = spsel_write },
     REGINFO_SENTINEL
 };
 
diff --git a/target-arm/internals.h b/target-arm/internals.h
index a527f02ff5..de79dfc316 100644
--- a/target-arm/internals.h
+++ b/target-arm/internals.h
@@ -60,6 +60,31 @@ enum arm_fprounding {
 
 int arm_rmode_to_sf(int rmode);
 
+static inline void update_spsel(CPUARMState *env, uint32_t imm)
+{
+    /* Update PSTATE SPSel bit; this requires us to update the
+     * working stack pointer in xregs[31].
+     */
+    if (!((imm ^ env->pstate) & PSTATE_SP)) {
+        return;
+    }
+    env->pstate = deposit32(env->pstate, 0, 1, imm);
+
+    /* EL0 has no access rights to update SPSel, and this code
+     * assumes we are updating SP for EL1 while running as EL1.
+     */
+    assert(arm_current_pl(env) == 1);
+    if (env->pstate & PSTATE_SP) {
+        /* Switch from using SP_EL0 to using SP_ELx */
+        env->sp_el[0] = env->xregs[31];
+        env->xregs[31] = env->sp_el[1];
+    } else {
+        /* Switch from SP_EL0 to SP_ELx */
+        env->sp_el[1] = env->xregs[31];
+        env->xregs[31] = env->sp_el[0];
+    }
+}
+
 /* Valid Syndrome Register EC field values */
 enum arm_exception_class {
     EC_UNCATEGORIZED          = 0x00,
diff --git a/target-arm/kvm64.c b/target-arm/kvm64.c
index ee727487b8..39c4364593 100644
--- a/target-arm/kvm64.c
+++ b/target-arm/kvm64.c
@@ -121,8 +121,24 @@ int kvm_arch_put_registers(CPUState *cs, int level)
         }
     }
 
+    /* KVM puts SP_EL0 in regs.sp and SP_EL1 in regs.sp_el1. On the
+     * QEMU side we keep the current SP in xregs[31] as well.
+     */
+    if (env->pstate & PSTATE_SP) {
+        env->sp_el[1] = env->xregs[31];
+    } else {
+        env->sp_el[0] = env->xregs[31];
+    }
+
     reg.id = AARCH64_CORE_REG(regs.sp);
-    reg.addr = (uintptr_t) &env->xregs[31];
+    reg.addr = (uintptr_t) &env->sp_el[0];
+    ret = kvm_vcpu_ioctl(cs, KVM_SET_ONE_REG, &reg);
+    if (ret) {
+        return ret;
+    }
+
+    reg.id = AARCH64_CORE_REG(sp_el1);
+    reg.addr = (uintptr_t) &env->sp_el[1];
     ret = kvm_vcpu_ioctl(cs, KVM_SET_ONE_REG, &reg);
     if (ret) {
         return ret;
@@ -152,7 +168,6 @@ int kvm_arch_put_registers(CPUState *cs, int level)
     }
 
     /* TODO:
-     * SP_EL1
      * SPSR[]
      * FP state
      * system registers
@@ -180,7 +195,14 @@ int kvm_arch_get_registers(CPUState *cs)
     }
 
     reg.id = AARCH64_CORE_REG(regs.sp);
-    reg.addr = (uintptr_t) &env->xregs[31];
+    reg.addr = (uintptr_t) &env->sp_el[0];
+    ret = kvm_vcpu_ioctl(cs, KVM_GET_ONE_REG, &reg);
+    if (ret) {
+        return ret;
+    }
+
+    reg.id = AARCH64_CORE_REG(sp_el1);
+    reg.addr = (uintptr_t) &env->sp_el[1];
     ret = kvm_vcpu_ioctl(cs, KVM_GET_ONE_REG, &reg);
     if (ret) {
         return ret;
@@ -194,6 +216,15 @@ int kvm_arch_get_registers(CPUState *cs)
     }
     pstate_write(env, val);
 
+    /* KVM puts SP_EL0 in regs.sp and SP_EL1 in regs.sp_el1. On the
+     * QEMU side we keep the current SP in xregs[31] as well.
+     */
+    if (env->pstate & PSTATE_SP) {
+        env->xregs[31] = env->sp_el[1];
+    } else {
+        env->xregs[31] = env->sp_el[0];
+    }
+
     reg.id = AARCH64_CORE_REG(regs.pc);
     reg.addr = (uintptr_t) &env->pc;
     ret = kvm_vcpu_ioctl(cs, KVM_GET_ONE_REG, &reg);
diff --git a/target-arm/machine.c b/target-arm/machine.c
index 42b1c90ac3..c2c0780d4f 100644
--- a/target-arm/machine.c
+++ b/target-arm/machine.c
@@ -222,9 +222,9 @@ static int cpu_post_load(void *opaque, int version_id)
 
 const VMStateDescription vmstate_arm_cpu = {
     .name = "cpu",
-    .version_id = 15,
-    .minimum_version_id = 15,
-    .minimum_version_id_old = 15,
+    .version_id = 16,
+    .minimum_version_id = 16,
+    .minimum_version_id_old = 16,
     .pre_save = cpu_pre_save,
     .post_load = cpu_post_load,
     .fields = (VMStateField[]) {
@@ -244,6 +244,7 @@ const VMStateDescription vmstate_arm_cpu = {
         VMSTATE_UINT32_ARRAY(env.usr_regs, ARMCPU, 5),
         VMSTATE_UINT32_ARRAY(env.fiq_regs, ARMCPU, 5),
         VMSTATE_UINT64(env.elr_el1, ARMCPU),
+        VMSTATE_UINT64_ARRAY(env.sp_el, ARMCPU, 2),
         /* The length-check must come before the arrays to avoid
          * incoming data possibly overflowing the array.
          */
diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
index 51edd9076c..64a33dd449 100644
--- a/target-arm/op_helper.c
+++ b/target-arm/op_helper.c
@@ -371,7 +371,7 @@ void HELPER(msr_i_pstate)(CPUARMState *env, uint32_t op, uint32_t imm)
 
     switch (op) {
     case 0x05: /* SPSel */
-        env->pstate = deposit32(env->pstate, 0, 1, imm);
+        update_spsel(env, imm);
         break;
     case 0x1e: /* DAIFSet */
         env->daif |= (imm << 6) & PSTATE_DAIF;