[PATCH v7 15/36] KVM: x86: Kill last_tsc_{nsec,write,offset} fields

From: David Woodhouse <[email protected]>

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.

Since cur_tsc_offset now serves as the single source of truth for the
TSC generation's offset, the backwards-TSC adjustment (used during S4
resume when the host TSC resets) must also update cur_tsc_offset by the
same delta applied to all vCPUs. Without this, subsequent vCPUs that
synchronize after the adjustment would get the stale pre-S4 offset.

Signed-off-by: David Woodhouse <[email protected]>
Reviewed-by: Paul Durrant <[email protected]>
---
 arch/x86/include/asm/kvm_host.h |  7 ++---
 arch/x86/kvm/x86.c              | 45 +++++++++++++++++----------------
 2 files changed, 25 insertions(+), 27 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index c3b97ca24a8c..2f01f3f9ba97 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1232,11 +1232,8 @@ 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 812657f7c984..dceb6d3660a2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1274,14 +1274,12 @@ 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;
 
@@ -1294,8 +1292,6 @@ 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;
@@ -1335,7 +1331,7 @@ void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 *user_value)
 	}
 
 	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) {
@@ -1345,7 +1341,7 @@ 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;
 			/*
@@ -1376,7 +1372,7 @@ 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, advance the reference point to "now"
 		 * so the matching window slides forward with each vCPU.
@@ -1644,7 +1640,7 @@ 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() * HZ_PER_KHZ;
 		if (tsc_hz && kvm_caps.has_tsc_control)
 			tsc_hz = kvm_scale_tsc(tsc_hz,
@@ -3376,8 +3372,8 @@ 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();
@@ -9748,7 +9744,7 @@ int kvm_arch_enable_virtualization_cpu(void)
 {
 	struct kvm *kvm;
 	struct kvm_vcpu *vcpu;
-	unsigned long i;
+	unsigned long i, flags;
 	int ret;
 	u64 local_tsc;
 	u64 max_tsc = 0;
@@ -9827,13 +9823,18 @@ int kvm_arch_enable_virtualization_cpu(void)
 			}
 
 			/*
-			 * We have to disable TSC offset matching.. if you were
-			 * booting a VM while issuing an S4 host suspend....
-			 * you may have some problem.  Solving this issue is
-			 * left as an exercise to the reader.
+			 * Adjust the TSC matching reference by the same
+			 * delta applied to each vCPU's offset, so that
+			 * future KVM_SET_TSC / vCPU creation still matches
+			 * correctly against the adjusted TSC timeline.
+			 * Scale from host to guest TSC rate.
 			 */
-			kvm->arch.last_tsc_nsec = 0;
-			kvm->arch.last_tsc_write = 0;
+			raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
+			kvm->arch.cur_tsc_write -=
+				kvm_scale_tsc(delta_cyc,
+					      kvm->arch.cur_tsc_scaling_ratio);
+			kvm->arch.cur_tsc_offset += delta_cyc;
+			raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
 		}
 
 	}
-- 
2.55.0