diff mbox series

[v15,6/9] arm64/kvm: Add hypercall service for kvm ptp.

Message ID 20201111062211.33144-7-jianyong.wu@arm.com (mailing list archive)
State Not Applicable
Delegated to: Netdev Maintainers
Headers show
Series Enable ptp_kvm for arm/arm64 | expand

Checks

Context Check Description
netdev/tree_selection success Not a local patch

Commit Message

Jianyong Wu Nov. 11, 2020, 6:22 a.m. UTC 
ptp_kvm will get this service through SMCC call.
The service offers wall time and cycle count of host to guest.
The caller must specify whether they want the host cycle count
or the difference between host cycle count and cntvoff.

Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
---
 arch/arm64/kvm/hypercalls.c | 61 +++++++++++++++++++++++++++++++++++++
 include/linux/arm-smccc.h   | 17 +++++++++++
 2 files changed, 78 insertions(+)

Comments

Marc Zyngier Nov. 23, 2020, 10:44 a.m. UTC | #1 
On 2020-11-11 06:22, Jianyong Wu wrote:
> ptp_kvm will get this service through SMCC call.
> The service offers wall time and cycle count of host to guest.
> The caller must specify whether they want the host cycle count
> or the difference between host cycle count and cntvoff.
> 
> Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
> ---
>  arch/arm64/kvm/hypercalls.c | 61 +++++++++++++++++++++++++++++++++++++
>  include/linux/arm-smccc.h   | 17 +++++++++++
>  2 files changed, 78 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
> index b9d8607083eb..f7d189563f3d 100644
> --- a/arch/arm64/kvm/hypercalls.c
> +++ b/arch/arm64/kvm/hypercalls.c
> @@ -9,6 +9,51 @@
>  #include <kvm/arm_hypercalls.h>
>  #include <kvm/arm_psci.h>
> 
> +static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val)
> +{
> +	struct system_time_snapshot systime_snapshot;
> +	u64 cycles = ~0UL;
> +	u32 feature;
> +
> +	/*
> +	 * system time and counter value must captured in the same
> +	 * time to keep consistency and precision.
> +	 */
> +	ktime_get_snapshot(&systime_snapshot);
> +
> +	// binding ptp_kvm clocksource to arm_arch_counter
> +	if (systime_snapshot.cs_id != CSID_ARM_ARCH_COUNTER)
> +		return;
> +
> +	val[0] = upper_32_bits(systime_snapshot.real);
> +	val[1] = lower_32_bits(systime_snapshot.real);

What is the endianness of these values? I can't see it defined
anywhere, and this is likely not to work if guest and hypervisor
don't align.

> +
> +	/*
> +	 * which of virtual counter or physical counter being
> +	 * asked for is decided by the r1 value of SMCCC
> +	 * call. If no invalid r1 value offered, default cycle
> +	 * value(-1) will be returned.
> +	 * Note: keep in mind that feature is u32 and smccc_get_arg1
> +	 * will return u64, so need auto cast here.
> +	 */
> +	feature = smccc_get_arg1(vcpu);
> +	switch (feature) {
> +	case ARM_PTP_VIRT_COUNTER:
> +		cycles = systime_snapshot.cycles - vcpu_read_sys_reg(vcpu, 
> CNTVOFF_EL2);
> +		break;
> +	case ARM_PTP_PHY_COUNTER:
> +		cycles = systime_snapshot.cycles;
> +		break;
> +	case ARM_PTP_NONE_COUNTER:

What is this "NONE" counter?

> +		break;
> +	default:
> +		val[0] = SMCCC_RET_NOT_SUPPORTED;
> +		break;
> +	}
> +	val[2] = upper_32_bits(cycles);
> +	val[3] = lower_32_bits(cycles);

Same problem as above.

> +}
> +
>  int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
>  {
>  	u32 func_id = smccc_get_function(vcpu);
> @@ -79,6 +124,22 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
>  		break;
>  	case ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID:
>  		val[0] = BIT(ARM_SMCCC_KVM_FUNC_FEATURES);
> +		val[0] |= BIT(ARM_SMCCC_KVM_FUNC_KVM_PTP);
> +		break;
> +	/*
> +	 * This serves virtual kvm_ptp.
> +	 * Four values will be passed back.
> +	 * reg0 stores high 32-bits of host ktime;
> +	 * reg1 stores low 32-bits of host ktime;
> +	 * For ARM_PTP_VIRT_COUNTER:
> +	 * reg2 stores high 32-bits of difference of host cycles and cntvoff;
> +	 * reg3 stores low 32-bits of difference of host cycles and cntvoff.
> +	 * For ARM_PTP_PHY_COUNTER:
> +	 * reg2 stores the high 32-bits of host cycles;
> +	 * reg3 stores the low 32-bits of host cycles.
> +	 */
> +	case ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID:
> +		kvm_ptp_get_time(vcpu, val);
>  		break;
>  	default:
>  		return kvm_psci_call(vcpu);
> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> index d75408141137..a03c5dd409d3 100644
> --- a/include/linux/arm-smccc.h
> +++ b/include/linux/arm-smccc.h
> @@ -103,6 +103,7 @@
> 
>  /* KVM "vendor specific" services */
>  #define ARM_SMCCC_KVM_FUNC_FEATURES		0
> +#define ARM_SMCCC_KVM_FUNC_KVM_PTP		1

I think having KVM once in the name is enough.

>  #define ARM_SMCCC_KVM_FUNC_FEATURES_2		127
>  #define ARM_SMCCC_KVM_NUM_FUNCS			128
> 
> @@ -114,6 +115,22 @@
> 
>  #define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED	1
> 
> +/*
> + * ptp_kvm is a feature used for time sync between vm and host.
> + * ptp_kvm module in guest kernel will get service from host using
> + * this hypercall ID.
> + */
> +#define ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID				\
> +	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
> +			   ARM_SMCCC_SMC_32,				\
> +			   ARM_SMCCC_OWNER_VENDOR_HYP,			\
> +			   ARM_SMCCC_KVM_FUNC_KVM_PTP)
> +
> +/* ptp_kvm counter type ID */
> +#define ARM_PTP_VIRT_COUNTER			0
> +#define ARM_PTP_PHY_COUNTER			1
> +#define ARM_PTP_NONE_COUNTER			2

The architecture definitely doesn't have this last counter.

> +
>  /* Paravirtualised time calls (defined by ARM DEN0057A) */
>  #define ARM_SMCCC_HV_PV_TIME_FEATURES				\
>  	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\

Thanks,

         M.
Marc Zyngier Nov. 23, 2020, 11:59 a.m. UTC | #2 
On 2020-11-23 10:44, Marc Zyngier wrote:
> On 2020-11-11 06:22, Jianyong Wu wrote:
>> ptp_kvm will get this service through SMCC call.
>> The service offers wall time and cycle count of host to guest.
>> The caller must specify whether they want the host cycle count
>> or the difference between host cycle count and cntvoff.
>> 
>> Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
>> ---
>>  arch/arm64/kvm/hypercalls.c | 61 
>> +++++++++++++++++++++++++++++++++++++
>>  include/linux/arm-smccc.h   | 17 +++++++++++
>>  2 files changed, 78 insertions(+)
>> 
>> diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
>> index b9d8607083eb..f7d189563f3d 100644
>> --- a/arch/arm64/kvm/hypercalls.c
>> +++ b/arch/arm64/kvm/hypercalls.c
>> @@ -9,6 +9,51 @@
>>  #include <kvm/arm_hypercalls.h>
>>  #include <kvm/arm_psci.h>
>> 
>> +static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val)
>> +{
>> +	struct system_time_snapshot systime_snapshot;
>> +	u64 cycles = ~0UL;
>> +	u32 feature;
>> +
>> +	/*
>> +	 * system time and counter value must captured in the same
>> +	 * time to keep consistency and precision.
>> +	 */
>> +	ktime_get_snapshot(&systime_snapshot);
>> +
>> +	// binding ptp_kvm clocksource to arm_arch_counter
>> +	if (systime_snapshot.cs_id != CSID_ARM_ARCH_COUNTER)
>> +		return;
>> +
>> +	val[0] = upper_32_bits(systime_snapshot.real);
>> +	val[1] = lower_32_bits(systime_snapshot.real);
> 
> What is the endianness of these values? I can't see it defined
> anywhere, and this is likely not to work if guest and hypervisor
> don't align.

Scratch that. This is all passed via registers, so the endianness
of the data is irrelevant. Please discard any comment about endianness
I made in this review.

The documentation aspect still requires to be beefed up.

Thanks,

         M.
Jianyong Wu Nov. 24, 2020, 5:11 a.m. UTC | #3 
Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Monday, November 23, 2020 7:59 PM
> To: Jianyong Wu <Jianyong.Wu@arm.com>
> Cc: Justin He <Justin.He@arm.com>; kvm@vger.kernel.org;
> netdev@vger.kernel.org; richardcochran@gmail.com; linux-
> kernel@vger.kernel.org; sean.j.christopherson@intel.com; Steven Price
> <Steven.Price@arm.com>; Andre Przywara <Andre.Przywara@arm.com>;
> john.stultz@linaro.org; yangbo.lu@nxp.com; pbonzini@redhat.com;
> tglx@linutronix.de; nd <nd@arm.com>; will@kernel.org;
> kvmarm@lists.cs.columbia.edu; linux-arm-kernel@lists.infradead.org
> Subject: Re: [PATCH v15 6/9] arm64/kvm: Add hypercall service for kvm ptp.
> 
> On 2020-11-23 10:44, Marc Zyngier wrote:
> > On 2020-11-11 06:22, Jianyong Wu wrote:
> >> ptp_kvm will get this service through SMCC call.
> >> The service offers wall time and cycle count of host to guest.
> >> The caller must specify whether they want the host cycle count or the
> >> difference between host cycle count and cntvoff.
> >>
> >> Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
> >> ---
> >>  arch/arm64/kvm/hypercalls.c | 61
> >> +++++++++++++++++++++++++++++++++++++
> >>  include/linux/arm-smccc.h   | 17 +++++++++++
> >>  2 files changed, 78 insertions(+)
> >>
> >> diff --git a/arch/arm64/kvm/hypercalls.c
> >> b/arch/arm64/kvm/hypercalls.c index b9d8607083eb..f7d189563f3d
> 100644
> >> --- a/arch/arm64/kvm/hypercalls.c
> >> +++ b/arch/arm64/kvm/hypercalls.c
> >> @@ -9,6 +9,51 @@
> >>  #include <kvm/arm_hypercalls.h>
> >>  #include <kvm/arm_psci.h>
> >>
> >> +static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val) {
> >> +	struct system_time_snapshot systime_snapshot;
> >> +	u64 cycles = ~0UL;
> >> +	u32 feature;
> >> +
> >> +	/*
> >> +	 * system time and counter value must captured in the same
> >> +	 * time to keep consistency and precision.
> >> +	 */
> >> +	ktime_get_snapshot(&systime_snapshot);
> >> +
> >> +	// binding ptp_kvm clocksource to arm_arch_counter
> >> +	if (systime_snapshot.cs_id != CSID_ARM_ARCH_COUNTER)
> >> +		return;
> >> +
> >> +	val[0] = upper_32_bits(systime_snapshot.real);
> >> +	val[1] = lower_32_bits(systime_snapshot.real);
> >
> > What is the endianness of these values? I can't see it defined
> > anywhere, and this is likely not to work if guest and hypervisor don't
> > align.
> 
> Scratch that. This is all passed via registers, so the endianness of the data is
> irrelevant. Please discard any comment about endianness I made in this
> review.
> 
Yeah, these data process and transfer are no relationship with endianness. Thanks.

> The documentation aspect still requires to be beefed up.

So the endianness description will be "no endianness restriction".

Thanks 
Jianyong

> 
> Thanks,
> 
>          M.
> --
> Jazz is not dead. It just smells funny...
Jianyong Wu Nov. 24, 2020, 5:20 a.m. UTC | #4 
Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Monday, November 23, 2020 6:44 PM
> To: Jianyong Wu <Jianyong.Wu@arm.com>
> Cc: netdev@vger.kernel.org; yangbo.lu@nxp.com; john.stultz@linaro.org;
> tglx@linutronix.de; pbonzini@redhat.com; sean.j.christopherson@intel.com;
> richardcochran@gmail.com; Mark Rutland <Mark.Rutland@arm.com>;
> will@kernel.org; Suzuki Poulose <Suzuki.Poulose@arm.com>; Andre
> Przywara <Andre.Przywara@arm.com>; Steven Price
> <Steven.Price@arm.com>; linux-kernel@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu;
> kvm@vger.kernel.org; Steve Capper <Steve.Capper@arm.com>; Justin He
> <Justin.He@arm.com>; nd <nd@arm.com>
> Subject: Re: [PATCH v15 6/9] arm64/kvm: Add hypercall service for kvm ptp.
> 
> On 2020-11-11 06:22, Jianyong Wu wrote:
> > ptp_kvm will get this service through SMCC call.
> > The service offers wall time and cycle count of host to guest.
> > The caller must specify whether they want the host cycle count or the
> > difference between host cycle count and cntvoff.
> >
> > Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
> > ---
> >  arch/arm64/kvm/hypercalls.c | 61
> +++++++++++++++++++++++++++++++++++++
> >  include/linux/arm-smccc.h   | 17 +++++++++++
> >  2 files changed, 78 insertions(+)
> >
> > diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
> > index b9d8607083eb..f7d189563f3d 100644
> > --- a/arch/arm64/kvm/hypercalls.c
> > +++ b/arch/arm64/kvm/hypercalls.c
> > @@ -9,6 +9,51 @@
> >  #include <kvm/arm_hypercalls.h>
> >  #include <kvm/arm_psci.h>
> >
> > +static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val) {
> > +	struct system_time_snapshot systime_snapshot;
> > +	u64 cycles = ~0UL;
> > +	u32 feature;
> > +
> > +	/*
> > +	 * system time and counter value must captured in the same
> > +	 * time to keep consistency and precision.
> > +	 */
> > +	ktime_get_snapshot(&systime_snapshot);
> > +
> > +	// binding ptp_kvm clocksource to arm_arch_counter
> > +	if (systime_snapshot.cs_id != CSID_ARM_ARCH_COUNTER)
> > +		return;
> > +
> > +	val[0] = upper_32_bits(systime_snapshot.real);
> > +	val[1] = lower_32_bits(systime_snapshot.real);
> 
> What is the endianness of these values? I can't see it defined anywhere, and
> this is likely not to work if guest and hypervisor don't align.
> 
> > +
> > +	/*
> > +	 * which of virtual counter or physical counter being
> > +	 * asked for is decided by the r1 value of SMCCC
> > +	 * call. If no invalid r1 value offered, default cycle
> > +	 * value(-1) will be returned.
> > +	 * Note: keep in mind that feature is u32 and smccc_get_arg1
> > +	 * will return u64, so need auto cast here.
> > +	 */
> > +	feature = smccc_get_arg1(vcpu);
> > +	switch (feature) {
> > +	case ARM_PTP_VIRT_COUNTER:
> > +		cycles = systime_snapshot.cycles - vcpu_read_sys_reg(vcpu,
> > CNTVOFF_EL2);
> > +		break;
> > +	case ARM_PTP_PHY_COUNTER:
> > +		cycles = systime_snapshot.cycles;
> > +		break;
> > +	case ARM_PTP_NONE_COUNTER:
> 
> What is this "NONE" counter?

Yeah, there is no counter named "NONE". this is not a counter, and only means no counter data needed for guest and just do nothing.
If no this arm here, it will go to the default one and return "NOT_SUPPORTED"

> 
> > +		break;
> > +	default:
> > +		val[0] = SMCCC_RET_NOT_SUPPORTED;
> > +		break;
> > +	}
> > +	val[2] = upper_32_bits(cycles);
> > +	val[3] = lower_32_bits(cycles);
> 
> Same problem as above.
> 
> > +}
> > +
> >  int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)  {
> >  	u32 func_id = smccc_get_function(vcpu); @@ -79,6 +124,22 @@ int
> > kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> >  		break;
> >  	case ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID:
> >  		val[0] = BIT(ARM_SMCCC_KVM_FUNC_FEATURES);
> > +		val[0] |= BIT(ARM_SMCCC_KVM_FUNC_KVM_PTP);
> > +		break;
> > +	/*
> > +	 * This serves virtual kvm_ptp.
> > +	 * Four values will be passed back.
> > +	 * reg0 stores high 32-bits of host ktime;
> > +	 * reg1 stores low 32-bits of host ktime;
> > +	 * For ARM_PTP_VIRT_COUNTER:
> > +	 * reg2 stores high 32-bits of difference of host cycles and cntvoff;
> > +	 * reg3 stores low 32-bits of difference of host cycles and cntvoff.
> > +	 * For ARM_PTP_PHY_COUNTER:
> > +	 * reg2 stores the high 32-bits of host cycles;
> > +	 * reg3 stores the low 32-bits of host cycles.
> > +	 */
> > +	case ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID:
> > +		kvm_ptp_get_time(vcpu, val);
> >  		break;
> >  	default:
> >  		return kvm_psci_call(vcpu);
> > diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> > index d75408141137..a03c5dd409d3 100644
> > --- a/include/linux/arm-smccc.h
> > +++ b/include/linux/arm-smccc.h
> > @@ -103,6 +103,7 @@
> >
> >  /* KVM "vendor specific" services */
> >  #define ARM_SMCCC_KVM_FUNC_FEATURES		0
> > +#define ARM_SMCCC_KVM_FUNC_KVM_PTP		1
> 
> I think having KVM once in the name is enough.
> 
> >  #define ARM_SMCCC_KVM_FUNC_FEATURES_2		127
> >  #define ARM_SMCCC_KVM_NUM_FUNCS			128
> >
> > @@ -114,6 +115,22 @@
> >
> >  #define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED	1
> >
> > +/*
> > + * ptp_kvm is a feature used for time sync between vm and host.
> > + * ptp_kvm module in guest kernel will get service from host using
> > + * this hypercall ID.
> > + */
> > +#define ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID
> 		\
> > +	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,
> 		\
> > +			   ARM_SMCCC_SMC_32,
> 	\
> > +			   ARM_SMCCC_OWNER_VENDOR_HYP,
> 		\
> > +			   ARM_SMCCC_KVM_FUNC_KVM_PTP)
> > +
> > +/* ptp_kvm counter type ID */
> > +#define ARM_PTP_VIRT_COUNTER			0
> > +#define ARM_PTP_PHY_COUNTER			1
> > +#define ARM_PTP_NONE_COUNTER			2
> 
> The architecture definitely doesn't have this last counter.

Yeah, this is just represent no counter data needed from guest.
Some annotation should be added here.

Thanks
Jianyong

> 
> > +
> >  /* Paravirtualised time calls (defined by ARM DEN0057A) */
> >  #define ARM_SMCCC_HV_PV_TIME_FEATURES
> 	\
> >  	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,
> 	\
> 
> Thanks,
> 
>          M.
> --
> Jazz is not dead. It just smells funny...
Marc Zyngier Nov. 24, 2020, 9:07 a.m. UTC | #5 
On 2020-11-24 05:20, Jianyong Wu wrote:
> Hi Marc,

[...]

>> > +/* ptp_kvm counter type ID */
>> > +#define ARM_PTP_VIRT_COUNTER			0
>> > +#define ARM_PTP_PHY_COUNTER			1
>> > +#define ARM_PTP_NONE_COUNTER			2
>> 
>> The architecture definitely doesn't have this last counter.
> 
> Yeah, this is just represent no counter data needed from guest.
> Some annotation should be added here.

I'd rather you remove it entirely, or explain why you really cannot
do without a fake counter.

         M.
Jianyong Wu Nov. 24, 2020, 10:14 a.m. UTC | #6 
Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Tuesday, November 24, 2020 5:07 PM
> To: Jianyong Wu <Jianyong.Wu@arm.com>
> Cc: netdev@vger.kernel.org; yangbo.lu@nxp.com; john.stultz@linaro.org;
> tglx@linutronix.de; pbonzini@redhat.com; sean.j.christopherson@intel.com;
> richardcochran@gmail.com; Mark Rutland <Mark.Rutland@arm.com>;
> will@kernel.org; Suzuki Poulose <Suzuki.Poulose@arm.com>; Andre
> Przywara <Andre.Przywara@arm.com>; Steven Price
> <Steven.Price@arm.com>; linux-kernel@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu;
> kvm@vger.kernel.org; Steve Capper <Steve.Capper@arm.com>; Justin He
> <Justin.He@arm.com>; nd <nd@arm.com>
> Subject: Re: [PATCH v15 6/9] arm64/kvm: Add hypercall service for kvm ptp.
> 
> On 2020-11-24 05:20, Jianyong Wu wrote:
> > Hi Marc,
> 
> [...]
> 
> >> > +/* ptp_kvm counter type ID */
> >> > +#define ARM_PTP_VIRT_COUNTER			0
> >> > +#define ARM_PTP_PHY_COUNTER			1
> >> > +#define ARM_PTP_NONE_COUNTER			2
> >>
> >> The architecture definitely doesn't have this last counter.
> >
> > Yeah, this is just represent no counter data needed from guest.
> > Some annotation should be added here.
> 
> I'd rather you remove it entirely, or explain why you really cannot do without
> a fake counter.

OK, I will remove it.

Thanks
Jianyong
> 
>          M.
> --
> Jazz is not dead. It just smells funny...
diff mbox series

Patch

diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index b9d8607083eb..f7d189563f3d 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -9,6 +9,51 @@ 
 #include <kvm/arm_hypercalls.h>
 #include <kvm/arm_psci.h>
 
+static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val)
+{
+	struct system_time_snapshot systime_snapshot;
+	u64 cycles = ~0UL;
+	u32 feature;
+
+	/*
+	 * system time and counter value must captured in the same
+	 * time to keep consistency and precision.
+	 */
+	ktime_get_snapshot(&systime_snapshot);
+
+	// binding ptp_kvm clocksource to arm_arch_counter
+	if (systime_snapshot.cs_id != CSID_ARM_ARCH_COUNTER)
+		return;
+
+	val[0] = upper_32_bits(systime_snapshot.real);
+	val[1] = lower_32_bits(systime_snapshot.real);
+
+	/*
+	 * which of virtual counter or physical counter being
+	 * asked for is decided by the r1 value of SMCCC
+	 * call. If no invalid r1 value offered, default cycle
+	 * value(-1) will be returned.
+	 * Note: keep in mind that feature is u32 and smccc_get_arg1
+	 * will return u64, so need auto cast here.
+	 */
+	feature = smccc_get_arg1(vcpu);
+	switch (feature) {
+	case ARM_PTP_VIRT_COUNTER:
+		cycles = systime_snapshot.cycles - vcpu_read_sys_reg(vcpu, CNTVOFF_EL2);
+		break;
+	case ARM_PTP_PHY_COUNTER:
+		cycles = systime_snapshot.cycles;
+		break;
+	case ARM_PTP_NONE_COUNTER:
+		break;
+	default:
+		val[0] = SMCCC_RET_NOT_SUPPORTED;
+		break;
+	}
+	val[2] = upper_32_bits(cycles);
+	val[3] = lower_32_bits(cycles);
+}
+
 int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 {
 	u32 func_id = smccc_get_function(vcpu);
@@ -79,6 +124,22 @@  int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 		break;
 	case ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID:
 		val[0] = BIT(ARM_SMCCC_KVM_FUNC_FEATURES);
+		val[0] |= BIT(ARM_SMCCC_KVM_FUNC_KVM_PTP);
+		break;
+	/*
+	 * This serves virtual kvm_ptp.
+	 * Four values will be passed back.
+	 * reg0 stores high 32-bits of host ktime;
+	 * reg1 stores low 32-bits of host ktime;
+	 * For ARM_PTP_VIRT_COUNTER:
+	 * reg2 stores high 32-bits of difference of host cycles and cntvoff;
+	 * reg3 stores low 32-bits of difference of host cycles and cntvoff.
+	 * For ARM_PTP_PHY_COUNTER:
+	 * reg2 stores the high 32-bits of host cycles;
+	 * reg3 stores the low 32-bits of host cycles.
+	 */
+	case ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID:
+		kvm_ptp_get_time(vcpu, val);
 		break;
 	default:
 		return kvm_psci_call(vcpu);
diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index d75408141137..a03c5dd409d3 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.h
@@ -103,6 +103,7 @@ 
 
 /* KVM "vendor specific" services */
 #define ARM_SMCCC_KVM_FUNC_FEATURES		0
+#define ARM_SMCCC_KVM_FUNC_KVM_PTP		1
 #define ARM_SMCCC_KVM_FUNC_FEATURES_2		127
 #define ARM_SMCCC_KVM_NUM_FUNCS			128
 
@@ -114,6 +115,22 @@ 
 
 #define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED	1
 
+/*
+ * ptp_kvm is a feature used for time sync between vm and host.
+ * ptp_kvm module in guest kernel will get service from host using
+ * this hypercall ID.
+ */
+#define ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID				\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
+			   ARM_SMCCC_SMC_32,				\
+			   ARM_SMCCC_OWNER_VENDOR_HYP,			\
+			   ARM_SMCCC_KVM_FUNC_KVM_PTP)
+
+/* ptp_kvm counter type ID */
+#define ARM_PTP_VIRT_COUNTER			0
+#define ARM_PTP_PHY_COUNTER			1
+#define ARM_PTP_NONE_COUNTER			2
+
 /* Paravirtualised time calls (defined by ARM DEN0057A) */
 #define ARM_SMCCC_HV_PV_TIME_FEATURES				\
 	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\