Commit 58d4277b authored by Oliver Upton's avatar Oliver Upton Committed by Paolo Bonzini
Browse files

KVM: x86: Refactor tsc synchronization code 



Refactor kvm_synchronize_tsc to make a new function that allows callers
to specify TSC parameters (offset, value, nanoseconds, etc.) explicitly
for the sake of participating in TSC synchronization.

Signed-off-by: default avatarOliver Upton <oupton@google.com>
Message-Id: <20210916181538.968978-7-oupton@google.com>
[Make sure kvm->arch.cur_tsc_generation and vcpu->arch.this_tsc_generation are
 equal at the end of __kvm_synchronize_tsc, if matched is false. Reported by
 Maxim Levitsky. - Paolo]
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 869b4421

arch/x86/kvm/x86.c

+53 −42
Original line number Diff line number Diff line
@@ -2435,13 +2435,63 @@ static inline bool kvm_check_tsc_unstable(void) 
	return check_tsc_unstable();

}



/*

 * Infers attempts to synchronize the guest's tsc from host writes. Sets the

 * offset for the vcpu and tracks the TSC matching generation that the vcpu

 * participates in.

 */

static void __kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 offset, u64 tsc,

				  u64 ns, bool matched)

{

	struct kvm *kvm = vcpu->kvm;



	lockdep_assert_held(&kvm->arch.tsc_write_lock);



	/*

	 * 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 = tsc;

	kvm->arch.last_tsc_khz = vcpu->arch.virtual_tsc_khz;



	vcpu->arch.last_guest_tsc = tsc;



	kvm_vcpu_write_tsc_offset(vcpu, offset);



	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.cur_tsc_generation++;

		kvm->arch.cur_tsc_nsec = ns;

		kvm->arch.cur_tsc_write = tsc;

		kvm->arch.cur_tsc_offset = offset;

		kvm->arch.nr_vcpus_matched_tsc = 0;

	} else if (vcpu->arch.this_tsc_generation != kvm->arch.cur_tsc_generation) {

		kvm->arch.nr_vcpus_matched_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_track_tsc_matching(vcpu);

}



static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 data)

{

	struct kvm *kvm = vcpu->kvm;

	u64 offset, ns, elapsed;

	unsigned long flags;

	bool matched;

	bool already_matched;

	bool matched = false;

	bool synchronizing = false;



	raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
@@ -2487,48 +2537,9 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 data) 
			offset = kvm_compute_l1_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;



	kvm_vcpu_write_tsc_offset(vcpu, offset);



	if (!matched) {

		kvm->arch.nr_vcpus_matched_tsc = 0;

	} else if (!already_matched) {

		kvm->arch.nr_vcpus_matched_tsc++;

	}



	kvm_track_tsc_matching(vcpu);

	__kvm_synchronize_tsc(vcpu, offset, data, ns, matched);

	raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);

}