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Commit 55dd00a7 authored by Marcelo Tosatti's avatar Marcelo Tosatti Committed by Paolo Bonzini
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KVM: x86: add KVM_HC_CLOCK_PAIRING hypercall 



Add a hypercall to retrieve the host realtime clock and the TSC value
used to calculate that clock read.

Used to implement clock synchronization between host and guest.

Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 6342c50a

Documentation/virtual/kvm/hypercalls.txt

+35 −0
Original line number Diff line number Diff line
@@ -81,3 +81,38 @@ the vcpu to sleep until occurrence of an appropriate event. Another vcpu of the 
same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,

specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)

is used in the hypercall for future use.





6. KVM_HC_CLOCK_PAIRING

------------------------

Architecture: x86

Status: active

Purpose: Hypercall used to synchronize host and guest clocks.

Usage:



a0: guest physical address where host copies

"struct kvm_clock_offset" structure.



a1: clock_type, ATM only KVM_CLOCK_PAIRING_WALLCLOCK (0)

is supported (corresponding to the host's CLOCK_REALTIME clock).



		struct kvm_clock_pairing {

			__s64 sec;

			__s64 nsec;

			__u64 tsc;

			__u32 flags;

			__u32 pad[9];

		};



       Where:

               * sec: seconds from clock_type clock.

               * nsec: nanoseconds from clock_type clock.

               * tsc: guest TSC value used to calculate sec/nsec pair

               * flags: flags, unused (0) at the moment.



The hypercall lets a guest compute a precise timestamp across

host and guest.  The guest can use the returned TSC value to

compute the CLOCK_REALTIME for its clock, at the same instant.



Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource,

or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK.

arch/x86/include/uapi/asm/kvm_para.h

+9 −0
Original line number Diff line number Diff line
@@ -50,6 +50,15 @@ struct kvm_steal_time { 
	__u32 pad[11];

};



#define KVM_CLOCK_PAIRING_WALLCLOCK 0

struct kvm_clock_pairing {

	__s64 sec;

	__s64 nsec;

	__u64 tsc;

	__u32 flags;

	__u32 pad[9];

};



#define KVM_STEAL_ALIGNMENT_BITS 5

#define KVM_STEAL_VALID_BITS ((-1ULL << (KVM_STEAL_ALIGNMENT_BITS + 1)))

#define KVM_STEAL_RESERVED_MASK (((1 << KVM_STEAL_ALIGNMENT_BITS) - 1 ) << 1)

arch/x86/kvm/x86.c

+66 −0
Original line number Diff line number Diff line
@@ -1142,6 +1142,7 @@ struct pvclock_gtod_data { 


	u64		boot_ns;

	u64		nsec_base;

	u64		wall_time_sec;

};



static struct pvclock_gtod_data pvclock_gtod_data;
@@ -1165,6 +1166,8 @@ static void update_pvclock_gtod(struct timekeeper *tk) 
	vdata->boot_ns			= boot_ns;

	vdata->nsec_base		= tk->tkr_mono.xtime_nsec;



	vdata->wall_time_sec            = tk->xtime_sec;



	write_seqcount_end(&vdata->seq);

}

#endif
@@ -1626,6 +1629,28 @@ static int do_monotonic_boot(s64 *t, u64 *cycle_now) 
	return mode;

}



static int do_realtime(struct timespec *ts, u64 *cycle_now)

{

	struct pvclock_gtod_data *gtod = &pvclock_gtod_data;

	unsigned long seq;

	int mode;

	u64 ns;



	do {

		seq = read_seqcount_begin(&gtod->seq);

		mode = gtod->clock.vclock_mode;

		ts->tv_sec = gtod->wall_time_sec;

		ns = gtod->nsec_base;

		ns += vgettsc(cycle_now);

		ns >>= gtod->clock.shift;

	} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));



	ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);

	ts->tv_nsec = ns;



	return mode;

}



/* returns true if host is using tsc clocksource */

static bool kvm_get_time_and_clockread(s64 *kernel_ns, u64 *cycle_now)

{
@@ -1635,6 +1660,17 @@ static bool kvm_get_time_and_clockread(s64 *kernel_ns, u64 *cycle_now) 


	return do_monotonic_boot(kernel_ns, cycle_now) == VCLOCK_TSC;

}



/* returns true if host is using tsc clocksource */

static bool kvm_get_walltime_and_clockread(struct timespec *ts,

					   u64 *cycle_now)

{

	/* checked again under seqlock below */

	if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)

		return false;



	return do_realtime(ts, cycle_now) == VCLOCK_TSC;

}

#endif



/*
@@ -6112,6 +6148,33 @@ int kvm_emulate_halt(struct kvm_vcpu *vcpu) 
}

EXPORT_SYMBOL_GPL(kvm_emulate_halt);



static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,

			        unsigned long clock_type)

{

	struct kvm_clock_pairing clock_pairing;

	struct timespec ts;

	cycle_t cycle;

	int ret;



	if (clock_type != KVM_CLOCK_PAIRING_WALLCLOCK)

		return -KVM_EOPNOTSUPP;



	if (kvm_get_walltime_and_clockread(&ts, &cycle) == false)

		return -KVM_EOPNOTSUPP;



	clock_pairing.sec = ts.tv_sec;

	clock_pairing.nsec = ts.tv_nsec;

	clock_pairing.tsc = kvm_read_l1_tsc(vcpu, cycle);

	clock_pairing.flags = 0;



	ret = 0;

	if (kvm_write_guest(vcpu->kvm, paddr, &clock_pairing,

			    sizeof(struct kvm_clock_pairing)))

		ret = -KVM_EFAULT;



	return ret;

}



/*

 * kvm_pv_kick_cpu_op:  Kick a vcpu.

 *
@@ -6176,6 +6239,9 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu) 
		kvm_pv_kick_cpu_op(vcpu->kvm, a0, a1);

		ret = 0;

		break;

	case KVM_HC_CLOCK_PAIRING:

		ret = kvm_pv_clock_pairing(vcpu, a0, a1);

		break;

	default:

		ret = -KVM_ENOSYS;

		break;

include/uapi/linux/kvm_para.h

+2 −0
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
#define KVM_EFAULT		EFAULT

#define KVM_E2BIG		E2BIG

#define KVM_EPERM		EPERM

#define KVM_EOPNOTSUPP		95



#define KVM_HC_VAPIC_POLL_IRQ		1

#define KVM_HC_MMU_OP			2
@@ -23,6 +24,7 @@ 
#define KVM_HC_MIPS_GET_CLOCK_FREQ	6

#define KVM_HC_MIPS_EXIT_VM		7

#define KVM_HC_MIPS_CONSOLE_OUTPUT	8

#define KVM_HC_CLOCK_PAIRING		9



/*

 * hypercalls use architecture specific