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Date: Wed, 25 Jan 2017 13:30:49 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Marcelo Tosatti <mtosatti@...hat.com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: 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 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];
> +};
> +
> #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.
> + };
> +
> + 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.
> + * 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.
> + 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.
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?
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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