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

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Date:   Mon, 23 Nov 2020 11:59:09 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Jianyong Wu <jianyong.wu@....com>
Cc:     justin.he@....com, kvm@...r.kernel.org, netdev@...r.kernel.org,
        richardcochran@...il.com, linux-kernel@...r.kernel.org,
        sean.j.christopherson@...el.com, steven.price@....com,
        Andre.Przywara@....com, john.stultz@...aro.org, yangbo.lu@....com,
        pbonzini@...hat.com, tglx@...utronix.de, nd@....com,
        will@...nel.org, kvmarm@...ts.cs.columbia.edu,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v15 6/9] arm64/kvm: Add hypercall service for kvm ptp.

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@....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...