kvm_write_tsc() determines when the host or guest is attempting to
synchronize the TSCs and does some bookkeeping for tracking this. Retain
the existing sync checks (host is writing 0 or TSCs being written within
a second of one another) in kvm_write_tsc(), but split off the
bookkeeping and TSC offset write into a new function. This allows for a
new ioctl to be introduced, yielding control of the TSC offset field to
userspace in a manner that respects the existing masterclock heuristics.
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>
Reviewed-by: Peter Shier <pshier@xxxxxxxxxx>
Signed-off-by: Oliver Upton <oupton@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 98 +++++++++++++++++++++++++---------------------
1 file changed, 54 insertions(+), 44 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e27d3db7e43f..a5c88f747da6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2045,13 +2045,64 @@ static inline bool kvm_check_tsc_unstable(void)
return check_tsc_unstable();
}
+/*
+ * Sets the TSC offset for the vCPU and tracks the TSC matching generation. Must
+ * hold the kvm->arch.tsc_write_lock to call this function.
+ */
+static void kvm_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset, u64 tsc,
+ u64 ns, bool matched)
+{
+ struct kvm *kvm = vcpu->kvm;
+ bool already_matched;
+
+ already_matched = (vcpu->arch.this_tsc_generation == kvm->arch.cur_tsc_generation);
+ /*
+ * We also track the most recent recorded KHZ, write and time to
+ * allow the matching interval to be extended at each write.
+ */
+ kvm->arch.last_tsc_nsec = ns;
+ kvm->arch.last_tsc_write = tsc;
+ kvm->arch.last_tsc_khz = vcpu->arch.virtual_tsc_khz;
+
+ vcpu->arch.last_guest_tsc = tsc;
+
+ /* Keep track of which generation this VCPU has synchronized to */
+ vcpu->arch.this_tsc_generation = kvm->arch.cur_tsc_generation;
+ vcpu->arch.this_tsc_nsec = kvm->arch.cur_tsc_nsec;
+ vcpu->arch.this_tsc_write = kvm->arch.cur_tsc_write;
+
+ kvm_vcpu_write_tsc_offset(vcpu, offset);
+
+ spin_lock(&kvm->arch.pvclock_gtod_sync_lock);
+ if (!matched) {
+ /*
+ * We split periods of matched TSC writes into generations.
+ * For each generation, we track the original measured
+ * nanosecond time, offset, and write, so if TSCs are in
+ * sync, we can match exact offset, and if not, we can match
+ * exact software computation in compute_guest_tsc()
+ *
+ * These values are tracked in kvm->arch.cur_xxx variables.
+ */
+ kvm->arch.nr_vcpus_matched_tsc = 0;
+ kvm->arch.cur_tsc_generation++;
+ kvm->arch.cur_tsc_nsec = ns;
+ kvm->arch.cur_tsc_write = tsc;
+ kvm->arch.cur_tsc_offset = offset;
+ } else if (!already_matched) {
+ kvm->arch.nr_vcpus_matched_tsc++;
+ }
+
+ kvm_track_tsc_matching(vcpu);
+ spin_unlock(&kvm->arch.pvclock_gtod_sync_lock);
+}
+
void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
{
struct kvm *kvm = vcpu->kvm;
u64 offset, ns, elapsed;
unsigned long flags;
- bool matched;
- bool already_matched;
+ bool matched = false;
u64 data = msr->data;
bool synchronizing = false;
@@ -2098,54 +2149,13 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
offset = kvm_compute_tsc_offset(vcpu, data);
}
matched = true;
- already_matched = (vcpu->arch.this_tsc_generation == kvm->arch.cur_tsc_generation);
- } else {
- /*
- * We split periods of matched TSC writes into generations.
- * For each generation, we track the original measured
- * nanosecond time, offset, and write, so if TSCs are in
- * sync, we can match exact offset, and if not, we can match
- * exact software computation in compute_guest_tsc()
- *
- * These values are tracked in kvm->arch.cur_xxx variables.
- */
- kvm->arch.cur_tsc_generation++;
- kvm->arch.cur_tsc_nsec = ns;
- kvm->arch.cur_tsc_write = data;
- kvm->arch.cur_tsc_offset = offset;
- matched = false;
}
- /*
- * We also track th most recent recorded KHZ, write and time to
- * allow the matching interval to be extended at each write.
- */
- kvm->arch.last_tsc_nsec = ns;
- kvm->arch.last_tsc_write = data;
- kvm->arch.last_tsc_khz = vcpu->arch.virtual_tsc_khz;
-
- vcpu->arch.last_guest_tsc = data;
-
- /* Keep track of which generation this VCPU has synchronized to */
- vcpu->arch.this_tsc_generation = kvm->arch.cur_tsc_generation;
- vcpu->arch.this_tsc_nsec = kvm->arch.cur_tsc_nsec;
- vcpu->arch.this_tsc_write = kvm->arch.cur_tsc_write;
-
if (!msr->host_initiated && guest_cpuid_has(vcpu, X86_FEATURE_TSC_ADJUST))
update_ia32_tsc_adjust_msr(vcpu, offset);
- kvm_vcpu_write_tsc_offset(vcpu, offset);
+ kvm_write_tsc_offset(vcpu, offset, data, ns, matched);
raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
-
- spin_lock(&kvm->arch.pvclock_gtod_sync_lock);
- if (!matched) {
- kvm->arch.nr_vcpus_matched_tsc = 0;
- } else if (!already_matched) {
- kvm->arch.nr_vcpus_matched_tsc++;
- }
-
- kvm_track_tsc_matching(vcpu);
- spin_unlock(&kvm->arch.pvclock_gtod_sync_lock);
}
EXPORT_SYMBOL_GPL(kvm_write_tsc);
--
2.28.0.rc0.142.g3c755180ce-goog
