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Commit c5e8ec8e authored by Denis Plotnikov's avatar Denis Plotnikov Committed by Radim Krčmář
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KVM: x86: remaster kvm_write_tsc code 



Reuse existing code instead of using inline asm.
Make the code more concise and clear in the TSC
synchronization part.

Signed-off-by: default avatarDenis Plotnikov <dplotnikov@virtuozzo.com>
Reviewed-by: default avatarRoman Kagan <rkagan@virtuozzo.com>
Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
parent 900ab14c

arch/x86/kvm/x86.c

+13 −39
Original line number Diff line number Diff line
@@ -1443,10 +1443,10 @@ 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;

	bool already_matched;

	u64 data = msr->data;

	bool synchronizing = false;



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

	offset = kvm_compute_tsc_offset(vcpu, data);
@@ -1454,51 +1454,25 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr) 
	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 */

		u64 tsc_exp = kvm->arch.last_tsc_write +

					nsec_to_cycles(vcpu, elapsed);

		u64 tsc_hz = vcpu->arch.virtual_tsc_khz * 1000LL;

		/*

		 * 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.

		 */

		synchronizing = data < tsc_exp + tsc_hz &&

				data + tsc_hz > tsc_exp;

	}



	/*

	 * 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 &&

	if (synchronizing &&

	    vcpu->arch.virtual_tsc_khz == kvm->arch.last_tsc_khz) {

		if (!check_tsc_unstable()) {

			offset = kvm->arch.cur_tsc_offset;