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Date: Wed, 25 Jan 2017 10:55:05 -0200
From: Marcelo Tosatti <mtosatti@...hat.com>
To: Paolo Bonzini <pbonzini@...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 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).
> > #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.
> > + };
> > +
> > + 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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