Re: [Qemu-devel] [RFC] arm/cpu: fix soft lockup panic after resuming from stop

[Heyi Guo]

Hi all,

I'm sorry this patch failed the docker-mingw@fedora build test. I'm going to 
move the code to target/arm/kvm.c.

Please ignore this one.

Thanks,

Heyi


On 2019/3/12 14:09, Heyi Guo wrote:

When we stop a VM for more than 30 seconds and then resume it, by qemu
monitor command "stop" and "cont", Linux on VM will complain of "soft
lockup - CPU#x stuck for xxs!" as below:

[ 2783.809517] watchdog: BUG: soft lockup - CPU#3 stuck for 2395s!
[ 2783.809559] watchdog: BUG: soft lockup - CPU#2 stuck for 2395s!
[ 2783.809561] watchdog: BUG: soft lockup - CPU#1 stuck for 2395s!
[ 2783.809563] Modules linked in...

This is because Guest Linux uses generic timer virtual counter as
a software watchdog, and CNTVCT_EL0 does not stop when VM is stopped
by qemu.

This patch is to fix this issue by saving the value of CNTVCT_EL0 when
stopping and restoring it when resuming.

Cc: Peter Maydell <peter.mayd...@linaro.org>
Signed-off-by: Heyi Guo <guoh...@huawei.com>
---
  target/arm/cpu.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  1 file changed, 65 insertions(+)

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 96f0ff0..7bbba3d 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -896,6 +896,60 @@ static void arm_cpu_finalizefn(Object *obj)
  #endif
  }

+static int get_vcpu_timer_tick(CPUState *cs, uint64_t *tick_at_pause)

+{
+    int err;
+    struct kvm_one_reg reg;
+
+    reg.id = KVM_REG_ARM_TIMER_CNT;
+    reg.addr = (uintptr_t) tick_at_pause;
+
+    err = kvm_vcpu_ioctl(cs, KVM_GET_ONE_REG, &reg);
+    return err;
+}
+
+static int set_vcpu_timer_tick(CPUState *cs, uint64_t tick_at_pause)
+{
+    int err;
+    struct kvm_one_reg reg;
+
+    reg.id = KVM_REG_ARM_TIMER_CNT;
+    reg.addr = (uintptr_t) &tick_at_pause;
+
+    err = kvm_vcpu_ioctl(cs, KVM_SET_ONE_REG, &reg);
+    return err;
+}
+
+static void arch_timer_change_state_handler(void *opaque, int running,
+                                            RunState state)
+{
+    static uint64_t hw_ticks_at_paused;
+    static RunState pre_state = RUN_STATE__MAX;
+    int err;
+    CPUState *cs = (CPUState *)opaque;
+
+    switch (state) {
+    case RUN_STATE_PAUSED:
+        err = get_vcpu_timer_tick(cs, &hw_ticks_at_paused);
+        if (err) {
+            error_report("Get vcpu timer tick failed: %d", err);
+        }
+        break;
+    case RUN_STATE_RUNNING:
+        if (pre_state == RUN_STATE_PAUSED) {
+            err = set_vcpu_timer_tick(cs, hw_ticks_at_paused);
+            if (err) {
+                error_report("Resume vcpu timer tick failed: %d", err);
+            }
+        }
+        break;
+    default:
+        break;
+    }
+
+    pre_state = state;
+}
+
  static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
  {
      CPUState *cs = CPU(dev);
@@ -906,6 +960,12 @@ static void arm_cpu_realizefn(DeviceState *dev, Error 
**errp)
      Error *local_err = NULL;
      bool no_aa32 = false;

+ /*

+     * Only add change state handler for arch timer once, for KVM will help to
+     * synchronize virtual timer of all VCPUs.
+     */
+    static bool arch_timer_change_state_handler_added;
+
      /* If we needed to query the host kernel for the CPU features
       * then it's possible that might have failed in the initfn, but
       * this is the first point where we can report it.
@@ -1181,6 +1241,11 @@ static void arm_cpu_realizefn(DeviceState *dev, Error 
**errp)

init_cpreg_list(cpu); + if (!arch_timer_change_state_handler_added && kvm_enabled()) {

+        qemu_add_vm_change_state_handler(arch_timer_change_state_handler, cs);
+        arch_timer_change_state_handler_added = true;
+    }
+
  #ifndef CONFIG_USER_ONLY
      if (cpu->has_el3 || arm_feature(env, ARM_FEATURE_M_SECURITY)) {
          cs->num_ases = 2;