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    Subject[PATCH 9/9] arm64: Retrieve stolen time as paravirtualized guest
    Date
    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 +++++++++++++++++++++++++++++++++++++
    include/linux/cpuhotplug.h | 1 +
    3 files changed, 157 insertions(+)
    create mode 100644 arch/arm64/kernel/kvm.c

    diff --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;
    +
    + 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;
    + }
    +
    + 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(&paravirt_steal_enabled);
    + if (steal_acc)
    + static_key_slow_inc(&paravirt_steal_rq_enabled);
    +
    + pr_info("using stolen time PV\n");
    +
    + return 0;
    +}
    +early_initcall(kvm_guest_init);
    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,
    --
    2.20.1
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