target/arm/kvm: Implement virtual time adjustment

When a VM is stopped (such as when it's paused) guest virtual time
should stop counting. Otherwise, when the VM is resumed it will
experience time jumps and its kernel may report soft lockups. Not
counting virtual time while the VM is stopped has the side effect
of making the guest's time appear to lag when compared with real
time, and even with time derived from the physical counter. For
this reason, this change, which is enabled by default, comes with
a KVM CPU feature allowing it to be disabled, restoring legacy
behavior.

This patch only provides the implementation of the virtual time
adjustment. A subsequent patch will provide the CPU property
allowing the change to be enabled and disabled.

Reported-by: Bijan Mottahedeh <bijan.mottahedeh@oracle.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>
Message-id: 20200120101023.16030-6-drjones@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/target/arm/machine.c b/target/arm/machine.c
index eb28b2381b..241890ac8c 100644
--- a/target/arm/machine.c
+++ b/target/arm/machine.c
@@ -642,6 +642,12 @@ static int cpu_pre_save(void *opaque)
             /* This should never fail */
             abort();
         }
+
+        /*
+         * kvm_arm_cpu_pre_save() must be called after
+         * write_kvmstate_to_list()
+         */
+        kvm_arm_cpu_pre_save(cpu);
     } else {
         if (!write_cpustate_to_list(cpu, false)) {
             /* This should never fail. */
@@ -744,6 +750,7 @@ static int cpu_post_load(void *opaque, int version_id)
          * we're using it.
          */
         write_list_to_cpustate(cpu);
+        kvm_arm_cpu_post_load(cpu);
     } else {
         if (!write_list_to_cpustate(cpu)) {
             return -1;