void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
{
	struct kvm *kvm = vcpu->kvm;
	u64 offset, ns, elapsed;
	unsigned long flags;
	s64 usdiff;
	bool matched;
	u64 data = msr->data;

	raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
	offset = kvm_x86_ops->compute_tsc_offset(vcpu, data);
	ns = get_kernel_ns();
	elapsed = ns - kvm->arch.last_tsc_nsec;

	if (vcpu->arch.virtual_tsc_khz) {
		int faulted = 0;

		/* n.b - signed multiplication and division required */
		usdiff = data - kvm->arch.last_tsc_write;
#ifdef CONFIG_X86_64
		usdiff = (usdiff * 1000) / vcpu->arch.virtual_tsc_khz;
#else
		/* do_div() only does unsigned */
		asm("1: idivl %[divisor]\n"
		    "2: xor %%edx, %%edx\n"
		    "   movl $0, %[faulted]\n"
		    "3:\n"
		    ".section .fixup,\"ax\"\n"
		    "4: movl $1, %[faulted]\n"
		    "   jmp  3b\n"
		    ".previous\n"

		_ASM_EXTABLE(1b, 4b)

		: "=A"(usdiff), [faulted] "=r" (faulted)
		: "A"(usdiff * 1000), [divisor] "rm"(vcpu->arch.virtual_tsc_khz));

#endif
		do_div(elapsed, 1000);
		usdiff -= elapsed;
		if (usdiff < 0)
			usdiff = -usdiff;

		/* idivl overflow => difference is larger than USEC_PER_SEC */
		if (faulted)
			usdiff = USEC_PER_SEC;
	} else
		usdiff = USEC_PER_SEC; /* disable TSC match window below */

	/*
	 * Special case: TSC write with a small delta (1 second) of virtual
	 * cycle time against real time is interpreted as an attempt to
	 * synchronize the CPU.
         *
	 * For a reliable TSC, we can match TSC offsets, and for an unstable
	 * TSC, we add elapsed time in this computation.  We could let the
	 * compensation code attempt to catch up if we fall behind, but
	 * it's better to try to match offsets from the beginning.
         */
	if (usdiff < USEC_PER_SEC &&
	    vcpu->arch.virtual_tsc_khz == kvm->arch.last_tsc_khz) {
		if (!check_tsc_unstable()) {
			offset = kvm->arch.cur_tsc_offset;
			pr_debug("kvm: matched tsc offset for %llu\n", data);
		} else {
			u64 delta = nsec_to_cycles(vcpu, elapsed);
			data += delta;
			offset = kvm_x86_ops->compute_tsc_offset(vcpu, data);
			pr_debug("kvm: adjusted tsc offset by %llu\n", delta);
		}
		matched = true;
	} 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;
		pr_debug("kvm: new tsc generation %u, clock %llu\n",
			 kvm->arch.cur_tsc_generation, data);
	}

	/*
	 * 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 (guest_cpuid_has_tsc_adjust(vcpu) && !msr->host_initiated)
		update_ia32_tsc_adjust_msr(vcpu, offset);
	kvm_x86_ops->write_tsc_offset(vcpu, offset);
	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++;
	else
		kvm->arch.nr_vcpus_matched_tsc = 0;

	kvm_track_tsc_matching(vcpu);
	spin_unlock(&kvm->arch.pvclock_gtod_sync_lock);
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.