[Qemu-devel] [PATCH uq/master] kvm: i8254: Finish time conversion fix

[Jan Kiszka]

0cdd3d1444 fixed reading back the counter load time from the kernel
while assuming the kernel would always update its load time on writing
the state. That is only true for channel 1, and so pit_get_channel_info
returned wrong output pin states for high counter values.

Fix this by applying the offset also on kvm_pit_put. For this purpose,
we cache the clock offset in KVMPITState, only updating it on VM state
changes or when we write the state while the VM is stopped.

Signed-off-by: Jan Kiszka <address@hidden>
---
 hw/kvm/i8254.c |   52 ++++++++++++++++++++++++++++++++++------------------
 1 files changed, 34 insertions(+), 18 deletions(-)

diff --git a/hw/kvm/i8254.c b/hw/kvm/i8254.c
index c5d3711..53d13e3 100644
--- a/hw/kvm/i8254.c
+++ b/hw/kvm/i8254.c
@@ -35,7 +35,8 @@
 typedef struct KVMPITState {
     PITCommonState pit;
     LostTickPolicy lost_tick_policy;
-    bool state_valid;
+    bool vm_stopped;
+    int64_t kernel_clock_offset;
 } KVMPITState;
 
 static int64_t abs64(int64_t v)
@@ -43,19 +44,11 @@ static int64_t abs64(int64_t v)
     return v < 0 ? -v : v;
 }
 
-static void kvm_pit_get(PITCommonState *pit)
+static void kvm_pit_update_clock_offset(KVMPITState *s)
 {
-    KVMPITState *s = DO_UPCAST(KVMPITState, pit, pit);
-    struct kvm_pit_state2 kpit;
-    struct kvm_pit_channel_state *kchan;
-    struct PITChannelState *sc;
     int64_t offset, clock_offset;
     struct timespec ts;
-    int i, ret;
-
-    if (s->state_valid) {
-        return;
-    }
+    int i;
 
     /*
      * Measure the delta between CLOCK_MONOTONIC, the base used for
@@ -72,6 +65,21 @@ static void kvm_pit_get(PITCommonState *pit)
             clock_offset = offset;
         }
     }
+    s->kernel_clock_offset = clock_offset;
+}
+
+static void kvm_pit_get(PITCommonState *pit)
+{
+    KVMPITState *s = DO_UPCAST(KVMPITState, pit, pit);
+    struct kvm_pit_state2 kpit;
+    struct kvm_pit_channel_state *kchan;
+    struct PITChannelState *sc;
+    int i, ret;
+
+    /* No need to re-read the state if VM is stopped. */
+    if (s->vm_stopped) {
+        return;
+    }
 
     if (kvm_has_pit_state2()) {
         ret = kvm_vm_ioctl(kvm_state, KVM_GET_PIT2, &kpit);
@@ -106,7 +114,7 @@ static void kvm_pit_get(PITCommonState *pit)
         sc->mode = kchan->mode;
         sc->bcd = kchan->bcd;
         sc->gate = kchan->gate;
-        sc->count_load_time = kchan->count_load_time + clock_offset;
+        sc->count_load_time = kchan->count_load_time + s->kernel_clock_offset;
     }
 
     sc = &pit->channels[0];
@@ -114,17 +122,23 @@ static void kvm_pit_get(PITCommonState *pit)
         pit_get_next_transition_time(sc, sc->count_load_time);
 }
 
-static void kvm_pit_put(PITCommonState *s)
+static void kvm_pit_put(PITCommonState *pit)
 {
+    KVMPITState *s = DO_UPCAST(KVMPITState, pit, pit);
     struct kvm_pit_state2 kpit;
     struct kvm_pit_channel_state *kchan;
     struct PITChannelState *sc;
     int i, ret;
 
-    kpit.flags = s->channels[0].irq_disabled ? KVM_PIT_FLAGS_HPET_LEGACY : 0;
+    /* The offset keeps changing as long as the VM is stopped. */
+    if (s->vm_stopped) {
+        kvm_pit_update_clock_offset(s);
+    }
+
+    kpit.flags = pit->channels[0].irq_disabled ? KVM_PIT_FLAGS_HPET_LEGACY : 0;
     for (i = 0; i < 3; i++) {
         kchan = &kpit.channels[i];
-        sc = &s->channels[i];
+        sc = &pit->channels[i];
         kchan->count = sc->count;
         kchan->latched_count = sc->latched_count;
         kchan->count_latched = sc->count_latched;
@@ -137,7 +151,7 @@ static void kvm_pit_put(PITCommonState *s)
         kchan->mode = sc->mode;
         kchan->bcd = sc->bcd;
         kchan->gate = sc->gate;
-        kchan->count_load_time = sc->count_load_time;
+        kchan->count_load_time = sc->count_load_time - s->kernel_clock_offset;
     }
 
     ret = kvm_vm_ioctl(kvm_state,
@@ -211,10 +225,12 @@ static void kvm_pit_vm_state_change(void *opaque, int 
running,
     KVMPITState *s = opaque;
 
     if (running) {
-        s->state_valid = false;
+        kvm_pit_update_clock_offset(s);
+        s->vm_stopped = false;
     } else {
+        kvm_pit_update_clock_offset(s);
         kvm_pit_get(&s->pit);
-        s->state_valid = true;
+        s->vm_stopped = true;
     }
 }
 
-- 
1.7.3.4