Re: [PATCH 9/9] arm64: Retrieve stolen time as paravirtualized guest
From: Marc Zyngier <maz@kernel.org>
Date: 2019-08-04 09:54:15
Also in:
kvm, kvmarm, linux-arm-kernel, lkml
On Fri, 2 Aug 2019 15:50:17 +0100 Steven Price [off-list ref] wrote:
Enable paravirtualization features when running under a hypervisor supporting the PV_TIME_ST hypercall. For each (v)CPU, we ask the hypervisor for the location of a shared page which the hypervisor will use to report stolen time to us. We set pv_time_ops to the stolen time function which simply reads the stolen value from the shared page for a VCPU. We guarantee single-copy atomicity using READ_ONCE which means we can also read the stolen time for another VCPU than the currently running one while it is potentially being updated by the hypervisor. Signed-off-by: Steven Price <steven.price@arm.com> --- arch/arm64/kernel/Makefile | 1 + arch/arm64/kernel/kvm.c | 155 +++++++++++++++++++++++++++++++++++++
nit: Why not using paravirt.c, which clearly states what it does? The alternative would be to name it kvm-pv.c.
quoted hunk ↗ jump to hunk
include/linux/cpuhotplug.h | 1 + 3 files changed, 157 insertions(+) create mode 100644 arch/arm64/kernel/kvm.cdiff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index 478491f07b4f..eb36edf9b930 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile@@ -63,6 +63,7 @@ obj-$(CONFIG_CRASH_CORE) += crash_core.o obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o obj-$(CONFIG_ARM64_SSBD) += ssbd.o obj-$(CONFIG_ARM64_PTR_AUTH) += pointer_auth.o +obj-$(CONFIG_PARAVIRT) += kvm.o obj-y += vdso/ probes/ obj-$(CONFIG_COMPAT_VDSO) += vdso32/diff --git a/arch/arm64/kernel/kvm.c b/arch/arm64/kernel/kvm.c new file mode 100644 index 000000000000..245398c79dae --- /dev/null +++ b/arch/arm64/kernel/kvm.c@@ -0,0 +1,155 @@ +// SPDX-License-Identifier: GPL-2.0 +// Copyright (C) 2019 Arm Ltd. + +#define pr_fmt(fmt) "kvmarm-pv: " fmt + +#include <linux/arm-smccc.h> +#include <linux/cpuhotplug.h> +#include <linux/io.h> +#include <linux/printk.h> +#include <linux/psci.h> +#include <linux/reboot.h> +#include <linux/slab.h> + +#include <asm/paravirt.h> +#include <asm/pvclock-abi.h> +#include <asm/smp_plat.h> + +struct kvmarm_stolen_time_region { + struct pvclock_vcpu_stolen_time_info *kaddr; +}; + +static DEFINE_PER_CPU(struct kvmarm_stolen_time_region, stolen_time_region); + +static bool steal_acc = true; +static int __init parse_no_stealacc(char *arg) +{ + steal_acc = false; + return 0; +} +early_param("no-steal-acc", parse_no_stealacc); + +/* return stolen time in ns by asking the hypervisor */ +static u64 kvm_steal_clock(int cpu) +{ + struct kvmarm_stolen_time_region *reg; + + reg = per_cpu_ptr(&stolen_time_region, cpu); + if (!reg->kaddr) { + pr_warn_once("stolen time enabled but not configured for cpu %d\n", + cpu); + return 0; + } + + return le64_to_cpu(READ_ONCE(reg->kaddr->stolen_time)); +} + +static int disable_stolen_time_current_cpu(void) +{ + struct kvmarm_stolen_time_region *reg; + + reg = this_cpu_ptr(&stolen_time_region); + if (!reg->kaddr) + return 0; + + memunmap(reg->kaddr); + memset(reg, 0, sizeof(*reg)); + + return 0; +} + +static int stolen_time_dying_cpu(unsigned int cpu) +{ + return disable_stolen_time_current_cpu(); +} + +static int init_stolen_time_cpu(unsigned int cpu) +{ + struct kvmarm_stolen_time_region *reg; + struct arm_smccc_res res; + + reg = this_cpu_ptr(&stolen_time_region); + + if (reg->kaddr) + return 0;
Can this actually happen? It'd take two CPU_UP calls from the HP notifiers to get in that situation...
+
+ arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_TIME_ST, &res);
+
+ if ((long)res.a0 < 0)
+ return -EINVAL;
+
+ reg->kaddr = memremap(res.a0,
+ sizeof(struct pvclock_vcpu_stolen_time_info),
+ MEMREMAP_WB);
+
+ if (reg->kaddr == NULL) {
+ pr_warn("Failed to map stolen time data structure\n");
+ return -EINVAL;-ENOMEM is the expected return code.
+ }
+
+ if (le32_to_cpu(reg->kaddr->revision) != 0 ||
+ le32_to_cpu(reg->kaddr->attributes) != 0) {
+ pr_warn("Unexpected revision or attributes in stolen time data\n");
+ return -ENXIO;
+ }
+
+ return 0;
+}
+
+static int kvm_arm_init_stolen_time(void)
+{
+ int ret;
+
+ ret = cpuhp_setup_state(CPUHP_AP_ARM_KVMPV_STARTING,
+ "hypervisor/kvmarm/pv:starting",
+ init_stolen_time_cpu, stolen_time_dying_cpu);
+ if (ret < 0)
+ return ret;
+ return 0;
+}
+
+static bool has_kvm_steal_clock(void)
+{
+ struct arm_smccc_res res;
+
+ /* To detect the presence of PV time support we require SMCCC 1.1+ */
+ if (psci_ops.smccc_version < SMCCC_VERSION_1_1)
+ return false;
+
+ arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
+ ARM_SMCCC_HV_PV_FEATURES, &res);
+
+ if (res.a0 != SMCCC_RET_SUCCESS)
+ return false;
+
+ arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_FEATURES,
+ ARM_SMCCC_HV_PV_TIME_ST, &res);
+
+ if (res.a0 != SMCCC_RET_SUCCESS)
+ return false;
+
+ return true;
+}
+
+static int __init kvm_guest_init(void)
+{
+ int ret = 0;
+
+ if (!has_kvm_steal_clock())
+ return 0;
+
+ ret = kvm_arm_init_stolen_time();
+ if (ret)
+ return ret;
+
+ pv_ops.time.steal_clock = kvm_steal_clock;
+
+ static_key_slow_inc(¶virt_steal_enabled);
+ if (steal_acc)
+ static_key_slow_inc(¶virt_steal_rq_enabled);
+
+ pr_info("using stolen time PV\n");
+
+ return 0;
+}
+early_initcall(kvm_guest_init);Is there any reason why we wouldn't directly call into this rather than using an initcall?
quoted hunk ↗ jump to hunk
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h index 068793a619ca..89d75edb5750 100644 --- a/include/linux/cpuhotplug.h +++ b/include/linux/cpuhotplug.h@@ -136,6 +136,7 @@ enum cpuhp_state { /* Must be the last timer callback */ CPUHP_AP_DUMMY_TIMER_STARTING, CPUHP_AP_ARM_XEN_STARTING, + CPUHP_AP_ARM_KVMPV_STARTING, CPUHP_AP_ARM_CORESIGHT_STARTING, CPUHP_AP_ARM64_ISNDEP_STARTING, CPUHP_AP_SMPCFD_DYING,
Thanks, M. -- Without deviation from the norm, progress is not possible.