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Message-ID: <aaead840-52c9-5b7f-1466-8a6c53f66f7d@redhat.com>
Date: Wed, 25 Jan 2017 13:59:34 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Marcelo Tosatti <mtosatti@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Radim Krcmar <rkrcmar@...hat.com>,
Richard Cochran <richardcochran@...il.com>,
Miroslav Lichvar <mlichvar@...hat.com>
Subject: Re: [patch 2/4] KVM: x86: add KVM_HC_CLOCK_OFFSET hypercall
On 25/01/2017 13:55, Marcelo Tosatti wrote:
> On Wed, Jan 25, 2017 at 01:30:49PM +0100, Paolo Bonzini wrote:
>>
>>
>> On 24/01/2017 18:09, Marcelo Tosatti wrote:
>>> Add a hypercall to retrieve the host realtime clock
>>> and the TSC value used to calculate that clock read.
>>>
>>> Used to implement clock synchronization between
>>> host and guest.
>>>
>>> Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
>>>
>>> ---
>>> Documentation/virtual/kvm/hypercalls.txt | 33 ++++++++++++++++++++++++
>>> arch/x86/include/uapi/asm/kvm_para.h | 9 ++++++
>>> arch/x86/kvm/x86.c | 41 +++++++++++++++++++++++++++++++
>>> include/uapi/linux/kvm_para.h | 3 ++
>>> 4 files changed, 86 insertions(+)
>>>
>>> v2: improve documentation (Radim)
>>> change hypercall name to KVM_HC_CLOCK_PAIRING (Radim)
>>> increase padding size
>>>
>>> Index: kvm-ptpdriver/arch/x86/include/uapi/asm/kvm_para.h
>>> ===================================================================
>>> --- kvm-ptpdriver.orig/arch/x86/include/uapi/asm/kvm_para.h 2017-01-13 16:43:11.947240575 -0200
>>> +++ kvm-ptpdriver/arch/x86/include/uapi/asm/kvm_para.h 2017-01-13 16:43:25.038258187 -0200
>>> @@ -50,6 +50,15 @@
>>> __u32 pad[11];
>>> };
>>>
>>> +#define KVM_CLOCK_PAIRING_WALLCLOCK 0
>>> +struct kvm_clock_offset {
>>
>> The struct still has the old name.
>>
>>> + __s64 sec;
>>> + __s64 nsec;
>>> + __u64 tsc;
>>> + __u32 flags;
>>> + __u32 pad[9];
>>> +};
>
> That was on purpose: "to pair" is the operation.
>
> "struct kvm_clock_pairing" makes no sense to me
> (because pairing is an "action").
>
> (if you'd prefer that name, let me know).
A "pairing" is a union of two things, in this case a sec/nsec value and
a TSC value. (I had to look it up in the dictionary though :)).
>>> #define KVM_STEAL_ALIGNMENT_BITS 5
>>> #define KVM_STEAL_VALID_BITS ((-1ULL << (KVM_STEAL_ALIGNMENT_BITS + 1)))
>>> #define KVM_STEAL_RESERVED_MASK (((1 << KVM_STEAL_ALIGNMENT_BITS) - 1 ) << 1)
>>> Index: kvm-ptpdriver/Documentation/virtual/kvm/hypercalls.txt
>>> ===================================================================
>>> --- kvm-ptpdriver.orig/Documentation/virtual/kvm/hypercalls.txt 2017-01-13 16:43:11.947240575 -0200
>>> +++ kvm-ptpdriver/Documentation/virtual/kvm/hypercalls.txt 2017-01-13 16:43:25.038258187 -0200
>>> @@ -81,3 +81,36 @@
>>> same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
>>> specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)
>>> is used in the hypercall for future use.
>>> +
>>> +
>>> +6. KVM_HC_CLOCK_PAIRING
>>> +------------------------
>>> +Architecture: x86
>>> +Status: active
>>> +Purpose: Hypercall used to synchronize host and guest clocks.
>>> +Usage:
>>> +
>>> +a0: guest physical address where host copies
>>> +"struct kvm_clock_offset" structure.
>>> +
>>> +a1: clock_type, ATM only KVM_CLOCK_PAIRING_WALLCLOCK (0)
>>> +is supported (hosts CLOCK_REALTIME clock).
>>> +
>>> + struct kvm_clock_offset {
>>
>> Name of the struct not adjusted.
>>> + __s64 sec;
>>> + __s64 nsec;
>>> + __u64 tsc;
>>> + __u32 flags;
>>> + __u32 pad[9];
>>
>> I'd just leave one element of padding and put the struct on the stack,
>> since we have no reason to think we'll need a lot of padding.
>
> Well you don't know: we could implement it in case of HPET clocksource
> hosts.
But then the guest wouldn't have a TSC value to use, would it?
Also, how would it use more padding?
Paolo
>>> + };
>>> +
>>> + Where:
>>> + * sec: seconds from clock_type clock.
>>> + * nsec: nanoseconds from clock_type clock.
>>> + * tsc: TSC value used to calculate sec/nsec pair
>>> + (this hypercall only works when host uses TSC clocksource).
>>
>> This is already mentioned below, and it's not clear that tsc is a guest
>> TSC value.
>
> Ok fixed.
>
>>> + * flags: flags, unused (0) at the moment.
>>> +
>>> +Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource,
>>> +or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK.
>>> +
>>> Index: kvm-ptpdriver/arch/x86/kvm/x86.c
>>> ===================================================================
>>> --- kvm-ptpdriver.orig/arch/x86/kvm/x86.c 2017-01-13 16:43:20.898252596 -0200
>>> +++ kvm-ptpdriver/arch/x86/kvm/x86.c 2017-01-13 16:43:25.041258191 -0200
>>> @@ -6119,6 +6119,44 @@
>>> }
>>> EXPORT_SYMBOL_GPL(kvm_emulate_halt);
>>>
>>> +static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,
>>> + unsigned long clock_type)
>>> +{
>>> + struct kvm_clock_offset *clock_offset;
>>> + struct timespec ts;
>>> + cycle_t cycle;
>>> + int ret;
>>> +
>>> + if (clock_type != KVM_CLOCK_PAIRING_WALLCLOCK)
>>> + return -KVM_EOPNOTSUPP;
>>> +
>>> + if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
>>> + return -KVM_EOPNOTSUPP;
>>
>> Already checked in kvm_get_walltime_and_clockread.
>
> Fixed.
>
>>> + clock_offset = kzalloc(sizeof(struct kvm_clock_offset), GFP_KERNEL);
>>> + if (clock_offset == NULL)
>>> + return -KVM_ENOMEM;
>>> +
>>> + if (kvm_get_walltime_and_clockread(&ts, &cycle) == false) {
>>> + kfree(clock_offset);
>>> + return -KVM_EOPNOTSUPP;
>>> + }
>>> + clock_offset->sec = ts.tv_sec;
>>> + clock_offset->nsec = ts.tv_nsec;
>>> + clock_offset->tsc = kvm_read_l1_tsc(vcpu, cycle);
>>> + clock_offset->flags = 0;
>>> +
>>> + ret = 0;
>>> + if (kvm_write_guest(vcpu->kvm, paddr, clock_offset,
>>> + sizeof(struct kvm_clock_offset)))
>>> + ret = -KVM_EFAULT;
>>> +
>>> + kfree(clock_offset);
>>> +
>>> + return ret;
>>> +}
>>> +
>>> /*
>>> * kvm_pv_kick_cpu_op: Kick a vcpu.
>>> *
>>> @@ -6183,6 +6221,9 @@
>>> kvm_pv_kick_cpu_op(vcpu->kvm, a0, a1);
>>> ret = 0;
>>> break;
>>> + case KVM_HC_CLOCK_PAIRING:
>>> + ret = kvm_pv_clock_pairing(vcpu, a0, a1);
>>> + break;
>>> default:
>>> ret = -KVM_ENOSYS;
>>> break;
>>> Index: kvm-ptpdriver/include/uapi/linux/kvm_para.h
>>> ===================================================================
>>> --- kvm-ptpdriver.orig/include/uapi/linux/kvm_para.h 2017-01-13 16:43:11.947240575 -0200
>>> +++ kvm-ptpdriver/include/uapi/linux/kvm_para.h 2017-01-13 16:43:25.042258192 -0200
>>> @@ -14,6 +14,8 @@
>>> #define KVM_EFAULT EFAULT
>>> #define KVM_E2BIG E2BIG
>>> #define KVM_EPERM EPERM
>>> +#define KVM_EOPNOTSUPP EOPNOTSUPP
>>> +#define KVM_ENOMEM ENOMEM
>>
>> This file could potentially be used across multiple architectures (it's
>> not in arch/x86/include/uapi/asm), but EOPNOTSUPP is not the same on
>> all systems. Better use "95" which is the value it has on x86.
>
> Fixed.
>
>> All this gives:
>>
>> diff --git a/Documentation/virtual/kvm/hypercalls.txt b/Documentation/virtual/kvm/hypercalls.txt
>> index 55eb3e1ca494..cd35de84999f 100644
>> --- a/Documentation/virtual/kvm/hypercalls.txt
>> +++ b/Documentation/virtual/kvm/hypercalls.txt
>> @@ -94,9 +94,9 @@ a0: guest physical address where host copies
>> "struct kvm_clock_offset" structure.
>>
>> a1: clock_type, ATM only KVM_CLOCK_PAIRING_WALLCLOCK (0)
>> -is supported (hosts CLOCK_REALTIME clock).
>> +is supported (corresponding to the host's CLOCK_REALTIME clock).
>>
>> - struct kvm_clock_offset {
>> + struct kvm_clock_pairing {
>> __s64 sec;
>> __s64 nsec;
>> __u64 tsc;
>> @@ -107,10 +107,12 @@ is supported (hosts CLOCK_REALTIME clock).
>> Where:
>> * sec: seconds from clock_type clock.
>> * nsec: nanoseconds from clock_type clock.
>> - * tsc: TSC value used to calculate sec/nsec pair
>> - (this hypercall only works when host uses TSC clocksource).
>> + * tsc: guest TSC value used to calculate sec/nsec pair
>> * flags: flags, unused (0) at the moment.
>>
>> +The hypercall lets a guest compute a precise timestamp across
>> +host and guest. The guest can use the returned TSC value to
>> +compute the CLOCK_REALTIME for its clock, at the same instant.
>> +
>> Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource,
>> or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK.
>> -
>> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
>> index ce7b411e28bc..3641d8b7dba9 100644
>> --- a/arch/x86/include/uapi/asm/kvm_para.h
>> +++ b/arch/x86/include/uapi/asm/kvm_para.h
>> @@ -51,12 +51,12 @@ struct kvm_steal_time {
>> };
>>
>> #define KVM_CLOCK_PAIRING_WALLCLOCK 0
>> -struct kvm_clock_offset {
>> +struct kvm_clock_pairing {
>> __s64 sec;
>> __s64 nsec;
>> __u64 tsc;
>> __u32 flags;
>> - __u32 pad[9];
>> + __u32 pad[1];
>> };
>>
>> #define KVM_STEAL_ALIGNMENT_BITS 5
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 4ecc3145ea4b..09e5d31dac98 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -6149,9 +6149,9 @@ int kvm_emulate_halt(struct kvm_vcpu *vcpu)
>> EXPORT_SYMBOL_GPL(kvm_emulate_halt);
>>
>> static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,
>> - unsigned long clock_type)
>> + unsigned long clock_type)
>> {
>> - struct kvm_clock_offset *clock_offset;
>> + struct kvm_clock_pairing clock_pairing;
>> struct timespec ts;
>> cycle_t cycle;
>> int ret;
>> @@ -6159,30 +6159,19 @@ static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,
>> if (clock_type != KVM_CLOCK_PAIRING_WALLCLOCK)
>> return -KVM_EOPNOTSUPP;
>>
>> - if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
>> - return -KVM_EOPNOTSUPP;
>> -
>> - clock_offset = kzalloc(sizeof(struct kvm_clock_offset), GFP_KERNEL);
>> - if (clock_offset == NULL)
>> - return -KVM_ENOMEM;
>> -
>> - if (kvm_get_walltime_and_clockread(&ts, &cycle) == false) {
>> - kfree(clock_offset);
>> + if (kvm_get_walltime_and_clockread(&ts, &cycle) == false)
>> return -KVM_EOPNOTSUPP;
>> - }
>>
>> - clock_offset->sec = ts.tv_sec;
>> - clock_offset->nsec = ts.tv_nsec;
>> - clock_offset->tsc = kvm_read_l1_tsc(vcpu, cycle);
>> - clock_offset->flags = 0;
>> + clock_pairing.sec = ts.tv_sec;
>> + clock_pairing.nsec = ts.tv_nsec;
>> + clock_pairing.tsc = kvm_read_l1_tsc(vcpu, cycle);
>> + clock_pairing.flags = 0;
>>
>> ret = 0;
>> - if (kvm_write_guest(vcpu->kvm, paddr, clock_offset,
>> - sizeof(struct kvm_clock_offset)))
>> + if (kvm_write_guest(vcpu->kvm, paddr, &clock_pairing,
>> + sizeof(struct kvm_clock_pairing)))
>> ret = -KVM_EFAULT;
>>
>> - kfree(clock_offset);
>> -
>> return ret;
>> }
>>
>> diff --git a/include/uapi/linux/kvm_para.h b/include/uapi/linux/kvm_para.h
>> index 68da60e7f519..c72128527377 100644
>> --- a/include/uapi/linux/kvm_para.h
>> +++ b/include/uapi/linux/kvm_para.h
>> @@ -14,7 +14,7 @@
>> #define KVM_EFAULT EFAULT
>> #define KVM_E2BIG E2BIG
>> #define KVM_EPERM EPERM
>> -#define KVM_EOPNOTSUPP EOPNOTSUPP
>> +#define KVM_EOPNOTSUPP 95
>> #define KVM_ENOMEM ENOMEM
>>
>> #define KVM_HC_VAPIC_POLL_IRQ 1
>>
>> Okay?
>
> Just not the padding please, the rest is fine.
>
>>
>> Paolo
>>
>>> #define KVM_HC_VAPIC_POLL_IRQ 1
>>> #define KVM_HC_MMU_OP 2
>>> @@ -23,6 +25,7 @@
>>> #define KVM_HC_MIPS_GET_CLOCK_FREQ 6
>>> #define KVM_HC_MIPS_EXIT_VM 7
>>> #define KVM_HC_MIPS_CONSOLE_OUTPUT 8
>>> +#define KVM_HC_CLOCK_PAIRING 9
>>>
>>> /*
>>> * hypercalls use architecture specific
>>>
>>>
>>>
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