Re: [PATCH v16 6/9] arm64/kvm: Add hypercall service for kvm ptp.
From: Marc Zyngier
Date: Tue Feb 02 2021 - 08:36:57 EST
On 2020-12-09 06:09, 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@xxxxxxx>
---
arch/arm64/kvm/hypercalls.c | 59 +++++++++++++++++++++++++++++++++++++
include/linux/arm-smccc.h | 16 ++++++++++
2 files changed, 75 insertions(+)
diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index b9d8607083eb..9a4834502388 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -9,6 +9,49 @@
#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);
+
+ /*
+ * which of virtual counter or physical counter being
+ * asked for is decided by the r1 value of SMCCC
+ * call. If no invalid r1 value offered, default cycle
+ * value(-1) will be returned.
+ * Note: keep in mind that feature is u32 and smccc_get_arg1
+ * will return u64, so need auto cast here.
This feels like a useless comment. On the other hand, you don't
document why we don't need to worry about -1 being used as the
top 32bits of the real time.
+ */
+ feature = smccc_get_arg1(vcpu);
+ switch (feature) {
+ case ARM_PTP_VIRT_COUNTER:
This #define should at least contain "KVM", because this isn't
something that is architectural.
+ cycles = systime_snapshot.cycles - vcpu_read_sys_reg(vcpu,
CNTVOFF_EL2);
+ break;
+ case ARM_PTP_PHY_COUNTER:
s/PHY/PHYS/
+ cycles = systime_snapshot.cycles;
+ break;
+ default:
+ val[0] = SMCCC_RET_NOT_SUPPORTED;
+ break;
+ }
+ val[2] = upper_32_bits(cycles);
+ val[3] = lower_32_bits(cycles);
The control flow is really odd. You start by writing values to
the return array, and then have to overwrite it if you fail.
I came up with the following instead (including comments):
@@ -16,38 +16,44 @@ static void kvm_ptp_get_time(struct kvm_vcpu *vcpu,
u64 *val)
u32 feature;
/*
- * system time and counter value must captured in the same
+ * system time and counter value must captured at the same
* time to keep consistency and precision.
*/
ktime_get_snapshot(&systime_snapshot);
- // binding ptp_kvm clocksource to arm_arch_counter
+ /*
+ * This is only valid if the current clocksource is the
+ * architected counter, as this is the only one the guest
+ * can see.
+ */
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);
-
/*
- * which of virtual counter or physical counter being
- * asked for is decided by the r1 value of SMCCC
- * call. If no invalid r1 value offered, default cycle
- * value(-1) will be returned.
- * Note: keep in mind that feature is u32 and smccc_get_arg1
- * will return u64, so need auto cast here.
+ * The guest selects one of the two reference counters
+ * (virtual or physical) with the first argument of the SMCCC
+ * call. In case the identifier is not supported, error out.
*/
feature = smccc_get_arg1(vcpu);
switch (feature) {
- case ARM_PTP_VIRT_COUNTER:
+ case KVM_PTP_VIRT_COUNTER:
cycles = systime_snapshot.cycles - vcpu_read_sys_reg(vcpu,
CNTVOFF_EL2);
break;
- case ARM_PTP_PHY_COUNTER:
+ case KVM_PTP_PHYS_COUNTER:
cycles = systime_snapshot.cycles;
break;
default:
- val[0] = SMCCC_RET_NOT_SUPPORTED;
- break;
+ return;
}
+
+ /*
+ * This relies on the top bit of val[0] never being set for
+ * valid values of system time, because that is *really* far
+ * in the future (about 292 years from 1970, and at that stage
+ * nobody will give a damn about it).
+ */
+ val[0] = upper_32_bits(systime_snapshot.real);
+ val[1] = lower_32_bits(systime_snapshot.real);
val[2] = upper_32_bits(cycles);
val[3] = lower_32_bits(cycles);
}
+}
+
int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
{
u32 func_id = smccc_get_function(vcpu);
@@ -79,6 +122,22 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
break;
case ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID:
val[0] = BIT(ARM_SMCCC_KVM_FUNC_FEATURES);
+ val[0] |= BIT(ARM_SMCCC_KVM_FUNC_PTP);
+ break;
+ /*
+ * This serves virtual kvm_ptp.
+ * Four values will be passed back.
+ * reg0 stores high 32-bits of host ktime;
+ * reg1 stores low 32-bits of host ktime;
+ * For ARM_PTP_VIRT_COUNTER:
+ * reg2 stores high 32-bits of difference of host cycles and cntvoff;
+ * reg3 stores low 32-bits of difference of host cycles and cntvoff.
+ * For ARM_PTP_PHY_COUNTER:
+ * reg2 stores the high 32-bits of host cycles;
+ * reg3 stores the low 32-bits of host cycles.
+ */
You have a patch with documentation in this series, and I don't think
this adds much.
+ case ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID:
+ kvm_ptp_get_time(vcpu, val);
break;
default:
return kvm_psci_call(vcpu);
diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index d75408141137..7924069f8f0a 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.h
@@ -103,6 +103,7 @@
/* KVM "vendor specific" services */
#define ARM_SMCCC_KVM_FUNC_FEATURES 0
+#define ARM_SMCCC_KVM_FUNC_PTP 1
#define ARM_SMCCC_KVM_FUNC_FEATURES_2 127
#define ARM_SMCCC_KVM_NUM_FUNCS 128
@@ -114,6 +115,21 @@
#define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED 1
+/*
+ * ptp_kvm is a feature used for time sync between vm and host.
+ * ptp_kvm module in guest kernel will get service from host using
+ * this hypercall ID.
+ */
+#define ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID \
+ ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \
+ ARM_SMCCC_SMC_32, \
+ ARM_SMCCC_OWNER_VENDOR_HYP, \
+ ARM_SMCCC_KVM_FUNC_PTP)
+
+/* ptp_kvm counter type ID */
+#define ARM_PTP_VIRT_COUNTER 0
+#define ARM_PTP_PHY_COUNTER 1
+#define KVM_PTP_VIRT_COUNTER 0
+#define KVM_PTP_PHYS_COUNTER 1
+
/* Paravirtualised time calls (defined by ARM DEN0057A) */
#define ARM_SMCCC_HV_PV_TIME_FEATURES \
ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \
Thanks,
M.
--
Jazz is not dead. It just smells funny...