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

[Marc Zyngier]

On 2020-11-23 10:44, Marc Zyngier wrote:
> 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@xxxxxxx>
> > ---
> >  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.

Scratch that. This is all passed via registers, so the endianness
of the data is irrelevant. Please discard any comment about endianness
I made in this review.

The documentation aspect still requires to be beefed up.

Thanks,

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