On Mon, Mar 9, 2015 at 8:26 AM, Christoffer Dall
[off-list ref] wrote:

On Wed, Mar 04, 2015 at 02:35:52PM +0000, Alex Benn?e wrote:

quoted

From: Christoffer Dall <redacted>

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 <redacted>
Signed-off-by: Alex Benn?e <redacted>

---
v2 (ajb)
  - minor tweaks and clarifications
v3
  - Use the correct bank index function for setting/getting env->spsr
  - only deal with spsrs in elevated exception levels

diff --git a/target-arm/kvm64.c b/target-arm/kvm64.c
index c60e989..45e5c3f 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 +207,27 @@ int kvm_arch_put_registers(CPUState *cs, int level)
         return ret;
     }

+    /* 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 (el > 0) {
+        if (is_a64(env)) {
+            g_assert(el == 1);
+            /* KVM only maps KVM_SPSR_SVC to KVM_SPSR_EL1 for aarch64 ATM */

not sure about the 'for aarch64' comment; I would say that it's for
aarch32 support.  Also, you can drop the ATM, since this is user space
ABI that we don't change easily.


don't you need to do env->banked_spsr[0] = env->spsr first?

I agree with Christoffer, env->spsr actually has the most current
value so you need to sync up with it before sending it out.

quoted

+            env->banked_spsr[1] = env->banked_spsr[0];

quoted

+        } else {
+            i = bank_number(env->uncached_cpsr & CPSR_M);
+            env->banked_spsr[i] = env->spsr;

so here we don't need to worry about banked_spsr[1] = banked_spsr[0]
because banked_spsr[0] is meaningless for 32-bit state and we only sync
banked_spsr[1] and up to KVM, correct?  I think this is what may deserve
a comment.

quoted

+        }
+    }
+
     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 +272,7 @@ 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 +345,35 @@ int kvm_arch_get_registers(CPUState *cs)
         return ret;
     }

+    /* 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

privilege

quoted

+     * there are some transitions possible which can access old state
+     * so it is worth keeping them all.
+     */

dubious comment overall

quoted

     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 (el > 0) {
+        if (is_a64(env)) {
+            g_assert(el == 1);
+            /* KVM maps KVM_SPSR_SVC to KVM_SPSR_EL1 for aarch64 */

same as above

If Christoffer's comment is referring to updating env->spsr, it occurs
below based on 'i'.

quoted

+            env->banked_spsr[0] = env->banked_spsr[1];
+            i = aarch64_banked_spsr_index(el);
+        } else {
+            i = bank_number(env->uncached_cpsr & CPSR_M);

same potential place for comment as above.

quoted

+        }
+        env->spsr = env->banked_spsr[i];
+    }
+
     /* Advanced SIMD and FP registers */
     for (i = 0; i < 32; i++) {
         reg.id = AARCH64_SIMD_CORE_REG(fp_regs.vregs[i]);
--
2.3.1