[RFC PATCH 3/5] target/arm/kvm: Implement cpu feature kvm-adjvtime

[Andrew Jones]

When kvm-adjvtime is enabled the guest's cntvct[_el0] won't count
the time when the VM is stopped. That time is skipped by updating
cntvoff[_el2] on each transition to vm_running using the current
QEMU_CLOCK_VIRTUAL time. QEMU_CLOCK_VIRTUAL only ticks when the VM
is running.

This patch only provides the implementation. A subsequent patch
will provide the CPU property allowing the feature to be enabled.

Reported-by: Bijan Mottahedeh <address@hidden>
Suggested-by: Bijan Mottahedeh <address@hidden>
Signed-off-by: Andrew Jones <address@hidden>
---
 target/arm/cpu.h     |  3 +++
 target/arm/kvm.c     | 20 ++++++++++++++++++++
 target/arm/kvm32.c   | 15 +++++++++++++++
 target/arm/kvm64.c   | 15 +++++++++++++++
 target/arm/kvm_arm.h | 12 ++++++++++++
 5 files changed, 65 insertions(+)

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index 5b9c3e4cd73d..923bd5e6384d 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -821,6 +821,9 @@ struct ARMCPU {
     /* KVM init features for this CPU */
     uint32_t kvm_init_features[7];
 
+    /* KVM CPU features */
+    bool kvm_adjvtime;
+
     /* Uniprocessor system with MP extensions */
     bool mp_is_up;
 
diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index 7a540d9591f9..f79b9b8ef57a 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -571,6 +571,26 @@ int kvm_arm_sync_mpstate_to_qemu(ARMCPU *cpu)
     return 0;
 }
 
+void kvm_arm_set_virtual_time(CPUState *cs)
+{
+    uint64_t cnt;
+    struct kvm_one_reg reg = {
+        .id = KVM_REG_ARM_TIMER_CNT,
+        .addr = (uintptr_t)&cnt,
+    };
+    int ret;
+
+    cnt = muldiv64(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL),
+                   cpu_get_host_tick_frequency(),
+                   NANOSECONDS_PER_SECOND);
+
+    ret = kvm_vcpu_ioctl(cs, KVM_SET_ONE_REG, &reg);
+    if (ret) {
+        error_report("Failed to set KVM_REG_ARM_TIMER_CNT");
+        abort();
+    }
+}
+
 int kvm_put_vcpu_events(ARMCPU *cpu)
 {
     CPUARMState *env = &cpu->env;
diff --git a/target/arm/kvm32.c b/target/arm/kvm32.c
index 32bf8d6757c4..79c6013066a9 100644
--- a/target/arm/kvm32.c
+++ b/target/arm/kvm32.c
@@ -16,6 +16,7 @@
 #include "qemu-common.h"
 #include "cpu.h"
 #include "qemu/timer.h"
+#include "sysemu/runstate.h"
 #include "sysemu/kvm.h"
 #include "kvm_arm.h"
 #include "internals.h"
@@ -183,6 +184,18 @@ int kvm_arm_cpreg_level(uint64_t regidx)
     return KVM_PUT_RUNTIME_STATE;
 }
 
+static void kvm_arm_vm_state_change(void *opaque, int running, RunState state)
+{
+    CPUState *cs = opaque;
+    ARMCPU *cpu = ARM_CPU(cs);
+
+    if (running) {
+        if (cpu->kvm_adjvtime) {
+            kvm_arm_set_virtual_time(cs);
+        }
+    }
+}
+
 #define ARM_CPU_ID_MPIDR       0, 0, 0, 5
 
 int kvm_arch_init_vcpu(CPUState *cs)
@@ -198,6 +211,8 @@ int kvm_arch_init_vcpu(CPUState *cs)
         return -EINVAL;
     }
 
+    qemu_add_vm_change_state_handler(kvm_arm_vm_state_change, cs);
+
     /* Determine init features for this CPU */
     memset(cpu->kvm_init_features, 0, sizeof(cpu->kvm_init_features));
     if (cpu->start_powered_off) {
diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
index 5cafcb7d36dd..494cf7f8a5cd 100644
--- a/target/arm/kvm64.c
+++ b/target/arm/kvm64.c
@@ -23,6 +23,7 @@
 #include "qemu/host-utils.h"
 #include "qemu/main-loop.h"
 #include "exec/gdbstub.h"
+#include "sysemu/runstate.h"
 #include "sysemu/kvm.h"
 #include "sysemu/kvm_int.h"
 #include "kvm_arm.h"
@@ -720,6 +721,18 @@ static int kvm_arm_sve_set_vls(CPUState *cs)
     return kvm_vcpu_ioctl(cs, KVM_SET_ONE_REG, &reg);
 }
 
+static void kvm_arm_vm_state_change(void *opaque, int running, RunState state)
+{
+    CPUState *cs = opaque;
+    ARMCPU *cpu = ARM_CPU(cs);
+
+    if (running) {
+        if (cpu->kvm_adjvtime) {
+            kvm_arm_set_virtual_time(cs);
+        }
+    }
+}
+
 #define ARM_CPU_ID_MPIDR       3, 0, 0, 0, 5
 
 int kvm_arch_init_vcpu(CPUState *cs)
@@ -735,6 +748,8 @@ int kvm_arch_init_vcpu(CPUState *cs)
         return -EINVAL;
     }
 
+    qemu_add_vm_change_state_handler(kvm_arm_vm_state_change, cs);
+
     /* Determine init features for this CPU */
     memset(cpu->kvm_init_features, 0, sizeof(cpu->kvm_init_features));
     if (cpu->start_powered_off) {
diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
index a1cc6513f72b..d506c4e84be6 100644
--- a/target/arm/kvm_arm.h
+++ b/target/arm/kvm_arm.h
@@ -232,6 +232,16 @@ void kvm_arm_sve_get_vls(CPUState *cs, unsigned long *map);
  */
 void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu);
 
+/**
+ * void kvm_arm_set_virtual_time:
+ * @cs: CPUState
+ *
+ * Sets the guest's virtual counter offset to the difference of the host's
+ * current time and QEMU's QEMU_CLOCK_VIRTUAL time. This allows the
+ * guest's virtual counter to only reflect VM running time.
+ */
+void kvm_arm_set_virtual_time(CPUState *cs);
+
 /**
  * kvm_arm_aarch32_supported:
  * @cs: CPUState
@@ -323,6 +333,8 @@ static inline int kvm_arm_vgic_probe(void)
     return 0;
 }
 
+static inline void kvm_arm_set_virtual_time(CPUState *cs) {}
+
 static inline void kvm_arm_pmu_set_irq(CPUState *cs, int irq) {}
 static inline void kvm_arm_pmu_init(CPUState *cs) {}
 
-- 
2.20.1