Factor out the actual updating of the kvm_clock in the guest memory from
preparing the values to be put there.
This paves the way to adding support for another kind of shared memory
clock (Hyper-V reference TSC page) that will use the same data.
Signed-off-by: Roman Kagan <rkagan@xxxxxxxxxxxxx>
---
arch/x86/kvm/x86.c | 117 ++++++++++++++++++++++++++++-------------------------
1 file changed, 62 insertions(+), 55 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9b7798c..a4a32ab 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1713,6 +1713,67 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)
#endif
}
+static void kvm_pvclock_update(struct kvm_vcpu *v, bool use_master_clock)
+{
+ struct kvm_vcpu_arch *vcpu = &v->arch;
+ struct pvclock_vcpu_time_info guest_hv_clock;
+ u8 pvclock_flags;
+
+ if (unlikely(kvm_read_guest_cached(v->kvm, &vcpu->pv_time,
+ &guest_hv_clock, sizeof(guest_hv_clock))))
+ return;
+
+ /* This VCPU is paused, but it's legal for a guest to read another
+ * VCPU's kvmclock, so we really have to follow the specification where
+ * it says that version is odd if data is being modified, and even after
+ * it is consistent.
+ *
+ * Version field updates must be kept separate. This is because
+ * kvm_write_guest_cached might use a "rep movs" instruction, and
+ * writes within a string instruction are weakly ordered. So there
+ * are three writes overall.
+ *
+ * As a small optimization, only write the version field in the first
+ * and third write. The vcpu->pv_time cache is still valid, because the
+ * version field is the first in the struct.
+ */
+ BUILD_BUG_ON(offsetof(struct pvclock_vcpu_time_info, version) != 0);
+
+ vcpu->hv_clock.version = guest_hv_clock.version + 1;
+ kvm_write_guest_cached(v->kvm, &vcpu->pv_time,
+ &vcpu->hv_clock,
+ sizeof(vcpu->hv_clock.version));
+
+ smp_wmb();
+
+ /* retain PVCLOCK_GUEST_STOPPED if set in guest copy */
+ pvclock_flags = (guest_hv_clock.flags & PVCLOCK_GUEST_STOPPED);
+
+ if (vcpu->pvclock_set_guest_stopped_request) {
+ pvclock_flags |= PVCLOCK_GUEST_STOPPED;
+ vcpu->pvclock_set_guest_stopped_request = false;
+ }
+
+ /* If the host uses TSC clocksource, then it is stable */
+ if (use_master_clock)
+ pvclock_flags |= PVCLOCK_TSC_STABLE_BIT;
+
+ vcpu->hv_clock.flags = pvclock_flags;
+
+ trace_kvm_pvclock_update(v->vcpu_id, &vcpu->hv_clock);
+
+ kvm_write_guest_cached(v->kvm, &vcpu->pv_time,
+ &vcpu->hv_clock,
+ sizeof(vcpu->hv_clock));
+
+ smp_wmb();
+
+ vcpu->hv_clock.version++;
+ kvm_write_guest_cached(v->kvm, &vcpu->pv_time,
+ &vcpu->hv_clock,
+ sizeof(vcpu->hv_clock.version));
+}
+
static int kvm_guest_time_update(struct kvm_vcpu *v)
{
unsigned long flags, tgt_tsc_khz;
@@ -1720,8 +1781,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
struct kvm_arch *ka = &v->kvm->arch;
s64 kernel_ns;
u64 tsc_timestamp, host_tsc;
- struct pvclock_vcpu_time_info guest_hv_clock;
- u8 pvclock_flags;
bool use_master_clock;
kernel_ns = 0;
@@ -1792,59 +1851,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset;
vcpu->last_guest_tsc = tsc_timestamp;
- if (unlikely(kvm_read_guest_cached(v->kvm, &vcpu->pv_time,
- &guest_hv_clock, sizeof(guest_hv_clock))))
- return 0;
-
- /* This VCPU is paused, but it's legal for a guest to read another
- * VCPU's kvmclock, so we really have to follow the specification where
- * it says that version is odd if data is being modified, and even after
- * it is consistent.
- *
- * Version field updates must be kept separate. This is because
- * kvm_write_guest_cached might use a "rep movs" instruction, and
- * writes within a string instruction are weakly ordered. So there
- * are three writes overall.
- *
- * As a small optimization, only write the version field in the first
- * and third write. The vcpu->pv_time cache is still valid, because the
- * version field is the first in the struct.
- */
- BUILD_BUG_ON(offsetof(struct pvclock_vcpu_time_info, version) != 0);
-
- vcpu->hv_clock.version = guest_hv_clock.version + 1;
- kvm_write_guest_cached(v->kvm, &vcpu->pv_time,
- &vcpu->hv_clock,
- sizeof(vcpu->hv_clock.version));
-
- smp_wmb();
-
- /* retain PVCLOCK_GUEST_STOPPED if set in guest copy */
- pvclock_flags = (guest_hv_clock.flags & PVCLOCK_GUEST_STOPPED);
-
- if (vcpu->pvclock_set_guest_stopped_request) {
- pvclock_flags |= PVCLOCK_GUEST_STOPPED;
- vcpu->pvclock_set_guest_stopped_request = false;
- }
-
- /* If the host uses TSC clocksource, then it is stable */
- if (use_master_clock)
- pvclock_flags |= PVCLOCK_TSC_STABLE_BIT;
-
- vcpu->hv_clock.flags = pvclock_flags;
-
- trace_kvm_pvclock_update(v->vcpu_id, &vcpu->hv_clock);
-
- kvm_write_guest_cached(v->kvm, &vcpu->pv_time,
- &vcpu->hv_clock,
- sizeof(vcpu->hv_clock));
-
- smp_wmb();
-
- vcpu->hv_clock.version++;
- kvm_write_guest_cached(v->kvm, &vcpu->pv_time,
- &vcpu->hv_clock,
- sizeof(vcpu->hv_clock.version));
+ kvm_pvclock_update(v, use_master_clock);
return 0;
}
--
2.5.5
--
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