[PATCH 5/6] target-arm/kvm64: fix save/restore of SPSR registers

[Alex Bennée]

From: Christoffer Dall <christoffer.dall at linaro.org>

The current code was negatively indexing the cpu state array and not
synchronizing banked spsr register state with the current mode's spsr
state, causing occasional failures with migration.

Some munging is done to take care of the aarch64 mapping and also to
ensure the most current value of the spsr is updated to the banked
registers (relevant for KVM<->TCG migration).

Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
Signed-off-by: Alex Bennée <alex.bennee at linaro.org>

---
v2 (ajb)
  - minor tweaks and clarifications

diff --git a/target-arm/kvm64.c b/target-arm/kvm64.c
index c60e989..6d30e10 100644
--- a/target-arm/kvm64.c
+++ b/target-arm/kvm64.c
@@ -140,6 +140,7 @@ int kvm_arch_put_registers(CPUState *cs, int level)
     uint64_t val;
     int i;
     int ret;
+    unsigned int el;
 
     ARMCPU *cpu = ARM_CPU(cs);
     CPUARMState *env = &cpu->env;
@@ -206,9 +207,25 @@ int kvm_arch_put_registers(CPUState *cs, int level)
         return ret;
     }
 
-    for (i = 0; i < KVM_NR_SPSR; i++) {
+    /* Saved Program State Registers
+     *
+     * Before we restore from the banked_spsr[] array we need to
+     * ensure that any modifications to env->spsr are correctly
+     * reflected and map aarch64 exception levels if required.
+     */
+    el = arm_current_el(env);
+    if (is_a64(env) && el > 0) {
+        g_assert(el == 1);
+        /* KVM maps KVM_SPSR_SVC to KVM_SPSR_EL1 for aarch64 */
+        env->banked_spsr[1] = env->banked_spsr[0];
+        env->banked_spsr[aarch64_banked_spsr_index(el)] = env->spsr;
+    } else {
+        env->banked_spsr[el] = env->spsr;
+    }
+
+    for (i=0; i<KVM_NR_SPSR; i++) {
         reg.id = AARCH64_CORE_REG(spsr[i]);
-        reg.addr = (uintptr_t) &env->banked_spsr[i - 1];
+        reg.addr = (uintptr_t) &env->banked_spsr[i+1];
         ret = kvm_vcpu_ioctl(cs, KVM_SET_ONE_REG, &reg);
         if (ret) {
             return ret;
@@ -253,6 +270,7 @@ int kvm_arch_get_registers(CPUState *cs)
     struct kvm_one_reg reg;
     uint64_t val;
     uint32_t fpr;
+    unsigned int el;
     int i;
     int ret;
 
@@ -325,15 +343,32 @@ int kvm_arch_get_registers(CPUState *cs)
         return ret;
     }
 
-    for (i = 0; i < KVM_NR_SPSR; i++) {
+    /* Fetch the SPSR registers
+     *
+     * KVM has an array of state indexed for all the possible aarch32
+     * privilage levels. Although not all are valid at all points
+     * there are some transitions possible which can access old state
+     * so it is worth keeping them all.
+     */
+    for (i=0; i<KVM_NR_SPSR; i++) {
         reg.id = AARCH64_CORE_REG(spsr[i]);
-        reg.addr = (uintptr_t) &env->banked_spsr[i - 1];
+        reg.addr = (uintptr_t) &env->banked_spsr[i+1];
         ret = kvm_vcpu_ioctl(cs, KVM_GET_ONE_REG, &reg);
         if (ret) {
             return ret;
         }
     }
 
+    el = arm_current_el(env);
+    if (is_a64(env) && el > 0) {
+        g_assert(el == 1);
+        /* KVM maps KVM_SPSR_SVC to KVM_SPSR_EL1 for aarch64 */
+        env->banked_spsr[0] = env->banked_spsr[1];
+        env->spsr = env->banked_spsr[aarch64_banked_spsr_index(el)];
+    } else {
+        env->spsr = env->banked_spsr[el];
+    }
+
     /* Advanced SIMD and FP registers */
     for (i = 0; i < 32; i++) {
         reg.id = AARCH64_SIMD_CORE_REG(fp_regs.vregs[i]);
-- 
2.3.0