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

Marc Zyngier
2020-11-23T10:44:38Z

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.
--
Jazz is not dead. It just smells funny...