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SubjectRE: [PATCH v14 07/10] arm64/kvm: Add hypercall service for kvm ptp.
Date
Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Saturday, September 5, 2020 12:15 AM
> 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>; 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 v14 07/10] arm64/kvm: Add hypercall service for kvm
> ptp.
>
> On Fri, 04 Sep 2020 10:27:41 +0100,
> Jianyong Wu <jianyong.wu@arm.com> wrote:
> >
> > ptp_kvm will get this service through smccc call.
> > The service offers wall time and counter cycle of host for guest.
> > caller must explicitly determines which cycle of virtual counter or
> > physical counter to return if it needs counter cycle.
> >
> > Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
> > ---
> > arch/arm64/kvm/Kconfig | 6 +++++
> > arch/arm64/kvm/arch_timer.c | 2 +-
> > arch/arm64/kvm/hypercalls.c | 49
> > ++++++++++++++++++++++++++++++++++++
> > include/kvm/arm_arch_timer.h | 1 +
> > include/linux/arm-smccc.h | 16 ++++++++++++
> > 5 files changed, 73 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig index
> > 318c8f2df245..bbdfacec4813 100644
> > --- a/arch/arm64/kvm/Kconfig
> > +++ b/arch/arm64/kvm/Kconfig
> > @@ -60,6 +60,12 @@ config KVM_ARM_PMU
> > config KVM_INDIRECT_VECTORS
> > def_bool HARDEN_BRANCH_PREDICTOR || RANDOMIZE_BASE
> >
> > +config ARM64_KVM_PTP_HOST
> > + bool "KVM PTP clock host service for arm64"
>
> The "for arm64" is not that useful.
Yeah,

>
> > + default y
> > + help
> > + virtual kvm ptp clock hypercall service for arm64
> > +
>
> I'm not keen on making this a compile option, because whatever is not
> always on ends up bit-rotting. Please drop the option.
>
Ok, I will remove this option next time.

> > endif # KVM
> >
> > endif # VIRTUALIZATION
> > diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
> > index 32ba6fbc3814..eb85f6701845 100644
> > --- a/arch/arm64/kvm/arch_timer.c
> > +++ b/arch/arm64/kvm/arch_timer.c
> > @@ -81,7 +81,7 @@ u64 timer_get_cval(struct arch_timer_context *ctxt)
> > }
> > }
> >
> > -static u64 timer_get_offset(struct arch_timer_context *ctxt)
> > +u64 timer_get_offset(struct arch_timer_context *ctxt)
> > {
> > struct kvm_vcpu *vcpu = ctxt->vcpu;
> >
> > diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
> > index 901c60f119c2..2628ddc13abd 100644
> > --- a/arch/arm64/kvm/hypercalls.c
> > +++ b/arch/arm64/kvm/hypercalls.c
> > @@ -3,6 +3,7 @@
> >
> > #include <linux/arm-smccc.h>
> > #include <linux/kvm_host.h>
> > +#include <linux/clocksource_ids.h>
> >
> > #include <asm/kvm_emulate.h>
> >
> > @@ -11,6 +12,10 @@
> >
> > int kvm_hvc_call_handler(struct kvm_vcpu *vcpu) {
> > +#ifdef CONFIG_ARM64_KVM_PTP_HOST
> > + struct system_time_snapshot systime_snapshot;
> > + u64 cycles = -1;
> > +#endif
>
> Please move all the PTP-related code to its own function, rather than
> keeping it in the main HVC dispatcher. Also assigning a negative value to
> something that is unsigned hurts my eyes. Consider using ~0UL instead.
> See the comment below though.

Ok, much better.

>
> > u32 func_id = smccc_get_function(vcpu);
> > u64 val[4] = {SMCCC_RET_NOT_SUPPORTED};
> > u32 feature;
> > @@ -21,6 +26,10 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> > val[0] = ARM_SMCCC_VERSION_1_1;
> > break;
> > case ARM_SMCCC_ARCH_FEATURES_FUNC_ID:
> > + /*
> > + * 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_SMCCC_ARCH_WORKAROUND_1:
> > @@ -70,7 +79,47 @@ 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);
> > +#ifdef CONFIG_ARM64_KVM_PTP_HOST
> > + val[0] |= BIT(ARM_SMCCC_KVM_FUNC_KVM_PTP); #endif
> > break;
> > +#ifdef CONFIG_ARM64_KVM_PTP_HOST
> > + /*
> > + * This serves virtual kvm_ptp.
> > + * Four values will be passed back.
> > + * reg0 stores high 32-bit host ktime;
> > + * reg1 stores low 32-bit host ktime;
> > + * reg2 stores high 32-bit difference of host cycles and cntvoff;
> > + * reg3 stores low 32-bit difference of host cycles and cntvoff.
>
> This comment doesn't match what I read below.
>
Sorry, should have changed according this time. But should keep this next time as
we really need use 32-bits value to support HVC32.

> > + */
> > + case ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID:
> > + /*
> > + * system time and counter value must captured in the same
> > + * time to keep consistency and precision.
> > + */
> > + ktime_get_snapshot(&systime_snapshot);
> > + if (systime_snapshot.cs_id != CSID_ARM_ARCH_COUNTER)
> > + break;
> > + val[0] = systime_snapshot.real;
> > + /*
> > + * which of virtual counter or physical counter being
> > + * asked for is decided by the r1 value of smccc
>
> nit: s/smccc/SMCCC/
Thanks

>
> > + * call. If no invalid r1 value offered, default cycle
>
> nit: If r1 is an invalid value...
>
> > + * value(-1) will return.
>
> nit: will be returned.
>
Yeah.

> > + */
> > + feature = smccc_get_arg1(vcpu);
> > + switch (feature) {
> > + case ARM_PTP_VIRT_COUNTER:
> > + cycles = systime_snapshot.cycles -
> > + vcpu_read_sys_reg(vcpu, CNTVOFF_EL2);
>
> nit: On a single line, please.
Ok.
>
> > + break;
> > + case ARM_PTP_PHY_COUNTER:
> > + cycles = systime_snapshot.cycles;
> > + break;
>
> It'd be a lot clearer if you had a default: case here, handling the invalid case.

Ok, much better.

>
> > + }
> > + val[1] = cycles;
>
> Given that cycles is a 64bit value, how does it work for a 32bit guest? Or have
> you removed support for 32bit guests altogether?
>
Yeah, I will arm32 support back.

Thanks
Jianyong
> > + break;
> > +#endif
> > default:
> > return kvm_psci_call(vcpu);
> > }
> > diff --git a/include/kvm/arm_arch_timer.h
> > b/include/kvm/arm_arch_timer.h index 51c19381108c..5a2b6da9be7a
> 100644
> > --- a/include/kvm/arm_arch_timer.h
> > +++ b/include/kvm/arm_arch_timer.h
> > @@ -105,5 +105,6 @@ void kvm_arm_timer_write_sysreg(struct
> kvm_vcpu
> > *vcpu,
> > /* Needed for tracing */
> > u32 timer_get_ctl(struct arch_timer_context *ctxt);
> > u64 timer_get_cval(struct arch_timer_context *ctxt);
> > +u64 timer_get_offset(struct arch_timer_context *ctxt);
> >
> > #endif
> > diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> > index f7b5dd7dbf9f..0724840eb5f7 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
> >
> > @@ -112,6 +113,21 @@
> > ARM_SMCCC_OWNER_VENDOR_HYP,
> \
> > ARM_SMCCC_KVM_FUNC_FEATURES)
> >
> > +/*
> > + * 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
> > +
> > /* Paravirtualised time calls (defined by ARM DEN0057A) */
> > #define ARM_SMCCC_HV_PV_TIME_FEATURES
> \
> > ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,
> \
> > --
> > 2.17.1
> >
> >
>
> Thanks,
>
> M.
>
> --
> Without deviation from the norm, progress is not possible.

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