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Date: Sun, 4 Aug 2019 10:53:53 +0100
From: Marc Zyngier <maz@...nel.org>
To: Steven Price <steven.price@....com>
Cc: Catalin Marinas <catalin.marinas@....com>,
Paolo Bonzini <pbonzini@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
Russell King <linux@...linux.org.uk>,
Will Deacon <will@...nel.org>,
James Morse <james.morse@....com>,
Julien Thierry <julien.thierry.kdev@...il.com>,
Suzuki K Pouloze <suzuki.poulose@....com>,
kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/9] arm64: Retrieve stolen time as paravirtualized
guest
On Fri, 2 Aug 2019 15:50:17 +0100
Steven Price <steven.price@....com> 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@....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.
> 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;
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?
> 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.
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