[PATCH v4 20/30] KVM: x86: Kill last_tsc_{nsec,write,offset} fields

[David Woodhouse <dwmw2@xxxxxxxxxxxxx>]

From: David Woodhouse <dwmw@xxxxxxxxxxxx>

These pointlessly duplicate the cur_tsc_{nsec,write,offset} values.
The only place they were used was where the TSC is stable and a new
vCPU is being synchronized to the previous setting, in which case the
cur_tsc_* value is definitely identical.

Rename last_tsc_khz and last_tsc_scaling_ratio to cur_tsc_khz and
cur_tsc_scaling_ratio respectively, since they are properties of the
current TSC generation.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Reviewed-by: Paul Durrant <paul@xxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  7 ++-----
 arch/x86/kvm/x86.c              | 32 ++++++++++++++------------------
 2 files changed, 16 insertions(+), 23 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5348fd5ea3f3..59298a8f78eb 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1486,11 +1486,8 @@ struct kvm_arch {
         * preemption-disabled region, so it must be a raw spinlock.
         */
        raw_spinlock_t tsc_write_lock;
-       u64 last_tsc_nsec;
-       u64 last_tsc_write;
-       u32 last_tsc_khz;
-       u64 last_tsc_offset;
-       u64 last_tsc_scaling_ratio;
+       u32 cur_tsc_khz;
+       u64 cur_tsc_scaling_ratio;
        u64 cur_tsc_nsec;
        u64 cur_tsc_write;
        u64 cur_tsc_offset;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 097df58749c3..3c68d2a4c8d0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2813,14 +2813,12 @@ static void __kvm_synchronize_tsc(struct kvm_vcpu 
*vcpu, u64 offset, u64 tsc,
                vcpu->kvm->arch.user_set_tsc = true;
 
        /*
-        * We also track th most recent recorded KHZ, write and time to
-        * allow the matching interval to be extended at each write.
+        * Track the TSC frequency, scaling ratio, and offset for the current
+        * generation. These are used to detect matching TSC writes and to
+        * compute the guest TSC from the host clock.
         */
-       kvm->arch.last_tsc_nsec = ns;
-       kvm->arch.last_tsc_write = tsc;
-       kvm->arch.last_tsc_khz = vcpu->arch.virtual_tsc_khz;
-       kvm->arch.last_tsc_offset = offset;
-       kvm->arch.last_tsc_scaling_ratio = vcpu->arch.l1_tsc_scaling_ratio;
+       kvm->arch.cur_tsc_khz = vcpu->arch.virtual_tsc_khz;
+       kvm->arch.cur_tsc_scaling_ratio = vcpu->arch.l1_tsc_scaling_ratio;
 
        vcpu->arch.last_guest_tsc = tsc;
 
@@ -2833,8 +2831,6 @@ static void __kvm_synchronize_tsc(struct kvm_vcpu *vcpu, 
u64 offset, u64 tsc,
                 * 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;
@@ -2873,7 +2869,7 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, 
u64 *user_value)
        raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
 
        offset = kvm_compute_l1_tsc_offset(vcpu, host_tsc, data);
-       elapsed = ns - kvm->arch.last_tsc_nsec;
+       elapsed = ns - kvm->arch.cur_tsc_nsec;
 
        if (vcpu->arch.virtual_tsc_khz) {
                if (data == 0) {
@@ -2883,7 +2879,7 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, 
u64 *user_value)
                         */
                        synchronizing = true;
                } else if (kvm->arch.user_set_tsc) {
-                       u64 tsc_exp = kvm->arch.last_tsc_write +
+                       u64 tsc_exp = kvm->arch.cur_tsc_write +
                                                nsec_to_cycles(vcpu, elapsed);
                        u64 tsc_hz = vcpu->arch.virtual_tsc_khz * 1000LL;
                        /*
@@ -2914,14 +2910,14 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, 
u64 *user_value)
         * it's better to try to match offsets from the beginning.
          */
        if (synchronizing &&
-           vcpu->arch.virtual_tsc_khz == kvm->arch.last_tsc_khz) {
+           vcpu->arch.virtual_tsc_khz == kvm->arch.cur_tsc_khz) {
                /*
                 * If synchronizing, the "last written" TSC value/time
                 * recorded by __kvm_synchronize_tsc() should not change
                 * (i.e. should be precisely the same as the existing
                 * generation).
                 */
-               data = kvm->arch.last_tsc_write;
+               data = kvm->arch.cur_tsc_write;
 
                if (!kvm_check_tsc_unstable()) {
                        offset = kvm->arch.cur_tsc_offset;
@@ -3206,7 +3202,7 @@ static void pvclock_update_vm_gtod_copy(struct kvm *kvm)
                 * get_kvmclock() to compute kvmclock from the host TSC
                 * without needing a vCPU reference.
                 */
-               ka->master_tsc_scaling_ratio = ka->last_tsc_scaling_ratio;
+               ka->master_tsc_scaling_ratio = ka->cur_tsc_scaling_ratio;
                tsc_hz = (u64)get_cpu_tsc_khz() * 1000;
                if (tsc_hz && kvm_caps.has_tsc_control)
                        tsc_hz = kvm_scale_tsc(tsc_hz,
@@ -6075,8 +6071,8 @@ static int kvm_arch_tsc_set_attr(struct kvm_vcpu *vcpu,
                raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
 
                matched = (vcpu->arch.virtual_tsc_khz &&
-                          kvm->arch.last_tsc_khz == vcpu->arch.virtual_tsc_khz 
&&
-                          kvm->arch.last_tsc_offset == offset);
+                          kvm->arch.cur_tsc_khz == vcpu->arch.virtual_tsc_khz 
&&
+                          kvm->arch.cur_tsc_offset == offset);
 
                tsc = kvm_scale_tsc(rdtsc(), vcpu->arch.l1_tsc_scaling_ratio) + 
offset;
                ns = get_kvmclock_base_ns();
@@ -13520,8 +13516,8 @@ int kvm_arch_enable_virtualization_cpu(void)
                         * you may have some problem.  Solving this issue is
                         * left as an exercise to the reader.
                         */
-                       kvm->arch.last_tsc_nsec = 0;
-                       kvm->arch.last_tsc_write = 0;
+                       kvm->arch.cur_tsc_nsec = 0;
+                       kvm->arch.cur_tsc_write = 0;
                }
 
        }
-- 
2.51.0