RE: [RFC PATCH v9 6/8] psci: Add hvc call service for ptp_kvm.

[Jianyong Wu <Jianyong.Wu@arm.com>]

Hi Marc,

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Tuesday, January 7, 2020 5:16 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>; 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>; Kaly Xin
> <Kaly.Xin@arm.com>; Justin He <Justin.He@arm.com>; nd <nd@arm.com>
> Subject: Re: [RFC PATCH v9 6/8] psci: Add hvc call service for ptp_kvm.
> 
> On 2019-12-10 03:40, Jianyong Wu wrote:
> > ptp_kvm modules will call hvc to get this service.
> > The service offers real time and counter cycle of host for guest.
> >
> > Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
> > ---
> >  include/linux/arm-smccc.h | 12 ++++++++++++
> >  virt/kvm/arm/psci.c       | 22 ++++++++++++++++++++++
> >  2 files changed, 34 insertions(+)
> >
> > diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> > index 6f82c87308ed..aafb6bac167d 100644
> > --- a/include/linux/arm-smccc.h
> > +++ b/include/linux/arm-smccc.h
> > @@ -94,6 +94,7 @@
> >
> >  /* KVM "vendor specific" services */
> >  #define ARM_SMCCC_KVM_FUNC_FEATURES		0
> > +#define ARM_SMCCC_KVM_PTP			1
> >  #define ARM_SMCCC_KVM_FUNC_FEATURES_2		127
> >  #define ARM_SMCCC_KVM_NUM_FUNCS			128
> >
> > @@ -103,6 +104,17 @@
> >  			   ARM_SMCCC_OWNER_VENDOR_HYP,
> 		\
> >  			   ARM_SMCCC_KVM_FUNC_FEATURES)
> >
> > +/*
> > + * This ID used for virtual ptp kvm clock and it will pass second
> > value
> > + * and nanosecond value of host real time and system counter by vcpu
> > + * register to guest.
> > + */
> > +#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_PTP)
> > +
> 
> All of this depends on patches that have never need posted to any ML, and
> just linger in Will's tree. You need to pick them up and post them as part of
> this series so that they can at least be reviewed.
> 
Ok, I will add them next version.

> >  #ifndef __ASSEMBLY__
> >
> >  #include <linux/linkage.h>
> > diff --git a/virt/kvm/arm/psci.c b/virt/kvm/arm/psci.c index
> > 0debf49bf259..682d892d6717 100644
> > --- a/virt/kvm/arm/psci.c
> > +++ b/virt/kvm/arm/psci.c
> > @@ -9,6 +9,7 @@
> >  #include <linux/kvm_host.h>
> >  #include <linux/uaccess.h>
> >  #include <linux/wait.h>
> > +#include <linux/clocksource_ids.h>
> >
> >  #include <asm/cputype.h>
> >  #include <asm/kvm_emulate.h>
> > @@ -389,6 +390,8 @@ static int kvm_psci_call(struct kvm_vcpu *vcpu)
> >
> >  int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)  {
> > +	struct system_time_snapshot systime_snapshot;
> > +	u64 cycles;
> >  	u32 func_id = smccc_get_function(vcpu);
> >  	u32 val[4] = {};
> >  	u32 option;
> > @@ -431,6 +434,25 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> >  	case ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID:
> >  		val[0] = BIT(ARM_SMCCC_KVM_FUNC_FEATURES);
> >  		break;
> > +	/*
> > +	 * This will used for virtual ptp kvm clock. three
> > +	 * 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.
> 
> That's either two or four values, and not three as you claim above.
> 
Sorry, I'm not sure what do you mean "three", the registers here is 4 from reg0 to reg3.

> Also, I fail to understand the meaning of the host cycle vs cntvoff comparison.
> This is something that guest can perform on its own (it has access to both
> physical and virtual timers, and can compute cntvoff without intervention of
> the hypervisor).
> 
To keep consistency and precision, clock time and counter cycle must captured at the same time. 
It will perform at ktime_get_snapshot.

> Finally, how does it work with nested virt, where cntvoff is for the the vEL2
> guest?
> 
For now, I have not considered ptp_kvm in nested virtualization. Also I'm not sure about if nested virtualization is
ready on arm64 , as I need test ptp_kvm on it. If so, I can consider it.

> > +	 */
> > +	case ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID:
> > +		ktime_get_snapshot(&systime_snapshot);
> > +		if (systime_snapshot.cs_id != CSID_ARM_ARCH_COUNTER)
> > +			return kvm_psci_call(vcpu);
> 
> What does this mean? Calling PSCI because you've failed to identify the clock
> source? What result do you expect from this? Hint: this isn't a PSCI call.
> 
Sorry, what I want to do here is that return to guest with the error info.
Maybe I should set val[0] to -1 and break to let the guest know that error comes, as
the guest will check if val[0] is positive to determine the next step.

> Cosmetic comments below:
> 
> > +		val[0] = systime_snapshot.real >> 32;
> 
> val[0] = upper_32_bits(systime_snapshot.real);
Ok
> 
> > +		val[1] = systime_snapshot.real << 32 >> 32;
> 
> val[1] = lower_32_bits(systime_snapshot.real);
> 
Yeah

> > +		cycles = systime_snapshot.cycles -
> > +			 vcpu_vtimer(vcpu)->cntvoff;
> 
> On a single line please.
>
ok
 
> > +		val[2] = cycles >> 32;
> > +		val[3] = cycles << 32 >> 32;
> 
> Same as above.
> 
yeah
> > +		break;
> >  	default:
> >  		return kvm_psci_call(vcpu);
> >  	}
> 

Thanks
Jianyong

> Thanks,
> 
>          M.
> --
> Jazz is not dead. It just smells funny...

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel