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

Marc Zyngier
2020-11-23T11:59:24Z

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@arm.com>
>> ---
>> 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...