Messages in this thread Patch in this message | | | Date | Tue, 02 Feb 2021 13:32:25 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH v16 6/9] arm64/kvm: Add hypercall service for kvm ptp. |
| |
On 2020-12-09 06:09, 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 | 59 +++++++++++++++++++++++++++++++++++++ > include/linux/arm-smccc.h | 16 ++++++++++ > 2 files changed, 75 insertions(+) > > diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c > index b9d8607083eb..9a4834502388 100644 > --- a/arch/arm64/kvm/hypercalls.c > +++ b/arch/arm64/kvm/hypercalls.c > @@ -9,6 +9,49 @@ > #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.
This feels like a useless comment. On the other hand, you don't document why we don't need to worry about -1 being used as the top 32bits of the real time.
> + */ > + feature = smccc_get_arg1(vcpu); > + switch (feature) { > + case ARM_PTP_VIRT_COUNTER:
This #define should at least contain "KVM", because this isn't something that is architectural.
> + cycles = systime_snapshot.cycles - vcpu_read_sys_reg(vcpu, > CNTVOFF_EL2); > + break; > + case ARM_PTP_PHY_COUNTER:
s/PHY/PHYS/
> + cycles = systime_snapshot.cycles; > + break; > + default: > + val[0] = SMCCC_RET_NOT_SUPPORTED; > + break; > + } > + val[2] = upper_32_bits(cycles); > + val[3] = lower_32_bits(cycles);
The control flow is really odd. You start by writing values to the return array, and then have to overwrite it if you fail.
I came up with the following instead (including comments):
@@ -16,38 +16,44 @@ static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val) u32 feature;
/* - * system time and counter value must captured in the same + * system time and counter value must captured at the same * time to keep consistency and precision. */ ktime_get_snapshot(&systime_snapshot);
- // binding ptp_kvm clocksource to arm_arch_counter + /* + * This is only valid if the current clocksource is the + * architected counter, as this is the only one the guest + * can see. + */ 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. + * The guest selects one of the two reference counters + * (virtual or physical) with the first argument of the SMCCC + * call. In case the identifier is not supported, error out. */ feature = smccc_get_arg1(vcpu); switch (feature) { - case ARM_PTP_VIRT_COUNTER: + case KVM_PTP_VIRT_COUNTER: cycles = systime_snapshot.cycles - vcpu_read_sys_reg(vcpu, CNTVOFF_EL2); break; - case ARM_PTP_PHY_COUNTER: + case KVM_PTP_PHYS_COUNTER: cycles = systime_snapshot.cycles; break; default: - val[0] = SMCCC_RET_NOT_SUPPORTED; - break; + return; } + + /* + * This relies on the top bit of val[0] never being set for + * valid values of system time, because that is *really* far + * in the future (about 292 years from 1970, and at that stage + * nobody will give a damn about it). + */ + val[0] = upper_32_bits(systime_snapshot.real); + val[1] = lower_32_bits(systime_snapshot.real); 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 +122,22 @@ 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_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. > + */
You have a patch with documentation in this series, and I don't think this adds much.
> + 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..7924069f8f0a 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_PTP 1 > #define ARM_SMCCC_KVM_FUNC_FEATURES_2 127 > #define ARM_SMCCC_KVM_NUM_FUNCS 128 > > @@ -114,6 +115,21 @@ > > #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_PTP) > + > +/* ptp_kvm counter type ID */ > +#define ARM_PTP_VIRT_COUNTER 0 > +#define ARM_PTP_PHY_COUNTER 1
+#define KVM_PTP_VIRT_COUNTER 0 +#define KVM_PTP_PHYS_COUNTER 1
> + > /* 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...
| |