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Date:   Mon, 7 Sep 2020 08:10:18 +0000
From:   Jianyong Wu <Jianyong.Wu@....com>
To:     Marc Zyngier <maz@...nel.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "yangbo.lu@....com" <yangbo.lu@....com>,
        "john.stultz@...aro.org" <john.stultz@...aro.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
        "richardcochran@...il.com" <richardcochran@...il.com>,
        Mark Rutland <Mark.Rutland@....com>,
        "will@...nel.org" <will@...nel.org>,
        Suzuki Poulose <Suzuki.Poulose@....com>,
        Steven Price <Steven.Price@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Steve Capper <Steve.Capper@....com>,
        Justin He <Justin.He@....com>, nd <nd@....com>
Subject: RE: [PATCH v14 07/10] arm64/kvm: Add hypercall service for kvm ptp.

Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@...nel.org>
> Sent: Saturday, September 5, 2020 12:15 AM
> To: Jianyong Wu <Jianyong.Wu@....com>
> Cc: netdev@...r.kernel.org; yangbo.lu@....com; john.stultz@...aro.org;
> tglx@...utronix.de; pbonzini@...hat.com; sean.j.christopherson@...el.com;
> richardcochran@...il.com; Mark Rutland <Mark.Rutland@....com>;
> will@...nel.org; Suzuki Poulose <Suzuki.Poulose@....com>; Steven Price
> <Steven.Price@....com>; linux-kernel@...r.kernel.org; linux-arm-
> kernel@...ts.infradead.org; kvmarm@...ts.cs.columbia.edu;
> kvm@...r.kernel.org; Steve Capper <Steve.Capper@....com>; Justin He
> <Justin.He@....com>; nd <nd@....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@....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@....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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