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From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Gavin Shan <gshan@redhat.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        james.morse@arm.com, mark.rutland@arm.com,
        Jonathan.Cameron@huawei.com, will@kernel.org, maz@kernel.org,
        pbonzini@redhat.com, shan.gavin@gmail.com,
        kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v4 14/15] arm64: Enable async PF
In-Reply-To: <20210815005947.83699-15-gshan@redhat.com>
References: <20210815005947.83699-1-gshan@redhat.com>
 <20210815005947.83699-15-gshan@redhat.com>
Date:   Mon, 16 Aug 2021 19:05:27 +0200
Message-ID: <878s11miaw.fsf@vitty.brq.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Gavin Shan <gshan@redhat.com> writes:

> This enables asynchronous page fault from guest side. The design
> is highlighted as below:
>
>    * The per-vCPU shared memory region, which is represented by
>      "struct kvm_vcpu_pv_apf_data", is allocated. The reason and
>      token associated with the received notifications of asynchronous
>      page fault are delivered through it.
>
>    * A per-vCPU table, which is represented by "struct kvm_apf_table",
>      is allocated. The process, on which the page-not-present notification
>      is received, is added into the table so that it can reschedule
>      itself on switching from kernel to user mode. Afterwards, the
>      process, identified by token, is removed from the table and put
>      into runnable state when page-ready notification is received.
>
>    * During CPU hotplug, the (private) SDEI event is expected to be
>      enabled or disabled on the affected CPU by SDEI client driver.
>      The (PPI) interrupt is enabled or disabled on the affected CPU
>      by ourself. When the system is going to reboot, the SDEI event
>      is disabled and unregistered and the (PPI) interrupt is disabled.
>
>    * The SDEI event and (PPI) interrupt number are retrieved from host
>      through SMCCC interface. Besides, the version of the asynchronous
>      page fault is validated when the feature is enabled on the guest.
>
>    * The feature is disabled on guest when boot parameter "no-kvmapf"
>      is specified.

Documentation/admin-guide/kernel-parameters.txt states this one is
x86-only:

        no-kvmapf       [X86,KVM] Disable paravirtualized asynchronous page
                        fault handling.

makes sense to update in this patch I believe.

>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  arch/arm64/kernel/Makefile |   1 +
>  arch/arm64/kernel/kvm.c    | 452 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 453 insertions(+)
>  create mode 100644 arch/arm64/kernel/kvm.c
>
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 3f1490bfb938..f0c1a6a7eaa7 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -59,6 +59,7 @@ obj-$(CONFIG_ACPI)			+= acpi.o
>  obj-$(CONFIG_ACPI_NUMA)			+= acpi_numa.o
>  obj-$(CONFIG_ARM64_ACPI_PARKING_PROTOCOL)	+= acpi_parking_protocol.o
>  obj-$(CONFIG_PARAVIRT)			+= paravirt.o
> +obj-$(CONFIG_KVM_GUEST)			+= kvm.o
>  obj-$(CONFIG_RANDOMIZE_BASE)		+= kaslr.o
>  obj-$(CONFIG_HIBERNATION)		+= hibernate.o hibernate-asm.o
>  obj-$(CONFIG_KEXEC_CORE)		+= machine_kexec.o relocate_kernel.o	\
> diff --git a/arch/arm64/kernel/kvm.c b/arch/arm64/kernel/kvm.c
> new file mode 100644
> index 000000000000..effe8dc7e921
> --- /dev/null
> +++ b/arch/arm64/kernel/kvm.c
> @@ -0,0 +1,452 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Asynchronous page fault support.
> + *
> + * Copyright (C) 2021 Red Hat, Inc.
> + *
> + * Author(s): Gavin Shan <gshan@redhat.com>
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/spinlock.h>
> +#include <linux/slab.h>
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/of.h>
> +#include <linux/of_fdt.h>
> +#include <linux/arm-smccc.h>
> +#include <linux/kvm_para.h>
> +#include <linux/arm_sdei.h>
> +#include <linux/acpi.h>
> +#include <linux/cpuhotplug.h>
> +#include <linux/reboot.h>
> +
> +struct kvm_apf_task {
> +	unsigned int		token;
> +	struct task_struct	*task;
> +	struct swait_queue_head	wq;
> +};
> +
> +struct kvm_apf_table {
> +	raw_spinlock_t		lock;
> +	unsigned int		count;
> +	struct kvm_apf_task	tasks[0];
> +};
> +
> +static bool async_pf_available = true;
> +static DEFINE_PER_CPU_DECRYPTED(struct kvm_vcpu_pv_apf_data, apf_data) __aligned(64);
> +static struct kvm_apf_table __percpu *apf_tables;
> +static unsigned int apf_tasks;
> +static unsigned int apf_sdei_num;
> +static unsigned int apf_ppi_num;
> +static int apf_irq;
> +
> +static bool kvm_async_pf_add_task(struct task_struct *task,
> +				  unsigned int token)
> +{
> +	struct kvm_apf_table *table = this_cpu_ptr(apf_tables);
> +	unsigned int i, index = apf_tasks;
> +	bool ret = false;
> +
> +	raw_spin_lock(&table->lock);
> +
> +	if (WARN_ON(table->count >= apf_tasks))
> +		goto unlock;
> +
> +	for (i = 0; i < apf_tasks; i++) {
> +		if (!table->tasks[i].task) {
> +			if (index == apf_tasks) {
> +				ret = true;
> +				index = i;
> +			}
> +		} else if (table->tasks[i].task == task) {
> +			WARN_ON(table->tasks[i].token != token);
> +			ret = false;
> +			break;
> +		}
> +	}
> +
> +	if (!ret)
> +		goto unlock;
> +
> +	task->thread.data = &table->tasks[index].wq;
> +	set_tsk_thread_flag(task, TIF_ASYNC_PF);
> +
> +	table->count++;
> +	table->tasks[index].task = task;
> +	table->tasks[index].token = token;
> +
> +unlock:
> +	raw_spin_unlock(&table->lock);
> +	return ret;
> +}
> +
> +static inline void kvm_async_pf_remove_one_task(struct kvm_apf_table *table,
> +						unsigned int index)
> +{
> +	clear_tsk_thread_flag(table->tasks[index].task, TIF_ASYNC_PF);
> +	WRITE_ONCE(table->tasks[index].task->thread.data, NULL);
> +
> +	table->count--;
> +	table->tasks[index].task = NULL;
> +	table->tasks[index].token = 0;
> +
> +	swake_up_one(&table->tasks[index].wq);
> +}
> +
> +static bool kvm_async_pf_remove_task(unsigned int token)
> +{
> +	struct kvm_apf_table *table = this_cpu_ptr(apf_tables);
> +	unsigned int i;
> +	bool ret = (token == UINT_MAX);
> +
> +	raw_spin_lock(&table->lock);
> +
> +	for (i = 0; i < apf_tasks; i++) {
> +		if (!table->tasks[i].task)
> +			continue;
> +
> +		/* Wakeup all */
> +		if (token == UINT_MAX) {
> +			kvm_async_pf_remove_one_task(table, i);
> +			continue;
> +		}
> +
> +		if (table->tasks[i].token == token) {
> +			kvm_async_pf_remove_one_task(table, i);
> +			ret = true;
> +			break;
> +		}
> +	}
> +
> +	raw_spin_unlock(&table->lock);
> +
> +	return ret;
> +}
> +
> +static int kvm_async_pf_sdei_handler(unsigned int event,
> +				     struct pt_regs *regs,
> +				     void *arg)
> +{
> +	unsigned int reason = __this_cpu_read(apf_data.reason);
> +	unsigned int token = __this_cpu_read(apf_data.token);
> +	bool ret;
> +
> +	if (reason != KVM_PV_REASON_PAGE_NOT_PRESENT) {
> +		pr_warn("%s: Bogus notification (%d, 0x%08x)\n",
> +			__func__, reason, token);
> +		return -EINVAL;
> +	}
> +
> +	ret = kvm_async_pf_add_task(current, token);
> +	__this_cpu_write(apf_data.token, 0);
> +	__this_cpu_write(apf_data.reason, 0);
> +
> +	if (!ret)
> +		return -ENOSPC;
> +
> +	smp_send_reschedule(smp_processor_id());
> +
> +	return 0;
> +}
> +
> +static irqreturn_t kvm_async_pf_irq_handler(int irq, void *dev_id)
> +{
> +	unsigned int reason = __this_cpu_read(apf_data.reason);
> +	unsigned int token = __this_cpu_read(apf_data.token);
> +	struct arm_smccc_res res;
> +
> +	if (reason != KVM_PV_REASON_PAGE_READY) {
> +		pr_warn("%s: Bogus interrupt %d (%d, 0x%08x)\n",
> +			__func__, irq, reason, token);

Spurrious interrupt or bogus APF reason set? Could be both I belive.

> +		return IRQ_HANDLED;
> +	}
> +
> +	kvm_async_pf_remove_task(token);
> +
> +	__this_cpu_write(apf_data.token, 0);
> +	__this_cpu_write(apf_data.reason, 0);
> +	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_ASYNC_PF_FUNC_ID,
> +			     ARM_SMCCC_KVM_FUNC_ASYNC_PF_IRQ_ACK, &res);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int __init kvm_async_pf_available(char *arg)
> +{
> +	async_pf_available = false;
> +
> +	return 0;
> +}
> +early_param("no-kvmapf", kvm_async_pf_available);
> +
> +static void kvm_async_pf_disable(void)
> +{
> +	struct arm_smccc_res res;
> +	u32 enabled = __this_cpu_read(apf_data.enabled);
> +
> +	if (!enabled)
> +		return;
> +
> +	/* Disable the functionality */
> +	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_ASYNC_PF_FUNC_ID,
> +			     ARM_SMCCC_KVM_FUNC_ASYNC_PF_ENABLE,
> +			     0, 0, &res);
> +	if (res.a0 != SMCCC_RET_SUCCESS) {
> +		pr_warn("%s: Error %ld to disable on CPU%d\n",
> +			__func__, res.a0, smp_processor_id());
> +		return;
> +	}
> +
> +	__this_cpu_write(apf_data.enabled, 0);
> +
> +	pr_info("Async PF disabled on CPU%d\n", smp_processor_id());

Nitpicking: x86 uses 

"setup async PF for cpu %d\n" and
"disable async PF for cpu %d\n"

which are not ideal maybe but in any case it would probably make sense
to be consistent across arches.


> +}
> +
> +static void kvm_async_pf_enable(void)
> +{
> +	struct arm_smccc_res res;
> +	u32 enabled = __this_cpu_read(apf_data.enabled);
> +	u64 val = virt_to_phys(this_cpu_ptr(&apf_data));
> +
> +	if (enabled)
> +		return;
> +
> +	val |= KVM_ASYNC_PF_ENABLED;
> +	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_ASYNC_PF_FUNC_ID,
> +			     ARM_SMCCC_KVM_FUNC_ASYNC_PF_ENABLE,
> +			     (u32)val, (u32)(val >> 32), &res);
> +	if (res.a0 != SMCCC_RET_SUCCESS) {
> +		pr_warn("%s: Error %ld to enable CPU%d\n",
> +			__func__, res.a0, smp_processor_id());
> +		return;
> +	}
> +
> +	__this_cpu_write(apf_data.enabled, 1);
> +
> +	pr_info("Async PF enabled on CPU%d\n", smp_processor_id());
> +}
> +
> +static void kvm_async_pf_cpu_disable(void *info)
> +{
> +	disable_percpu_irq(apf_irq);
> +	kvm_async_pf_disable();
> +}
> +
> +static void kvm_async_pf_cpu_enable(void *info)
> +{
> +	enable_percpu_irq(apf_irq, IRQ_TYPE_LEVEL_HIGH);
> +	kvm_async_pf_enable();
> +}
> +
> +static int kvm_async_pf_cpu_reboot_notify(struct notifier_block *nb,
> +					  unsigned long code,
> +					  void *unused)
> +{
> +	if (code == SYS_RESTART) {
> +		sdei_event_disable(apf_sdei_num);
> +		sdei_event_unregister(apf_sdei_num);
> +
> +		on_each_cpu(kvm_async_pf_cpu_disable, NULL, 1);
> +	}
> +
> +	return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block kvm_async_pf_cpu_reboot_nb = {
> +	.notifier_call = kvm_async_pf_cpu_reboot_notify,
> +};
> +
> +static int kvm_async_pf_cpu_online(unsigned int cpu)
> +{
> +	kvm_async_pf_cpu_enable(NULL);
> +
> +	return 0;
> +}
> +
> +static int kvm_async_pf_cpu_offline(unsigned int cpu)
> +{
> +	kvm_async_pf_cpu_disable(NULL);
> +
> +	return 0;
> +}
> +
> +static int __init kvm_async_pf_check_version(void)
> +{
> +	struct arm_smccc_res res;
> +
> +	/*
> +	 * Check the version and v1.0.0 or higher version is required
> +	 * to support the functionality.
> +	 */
> +	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_ASYNC_PF_FUNC_ID,
> +			     ARM_SMCCC_KVM_FUNC_ASYNC_PF_VERSION, &res);
> +	if (res.a0 != SMCCC_RET_SUCCESS) {
> +		pr_warn("%s: Error %ld to get version\n",
> +			__func__, res.a0);
> +		return -EPERM;
> +	}
> +
> +	if ((res.a1 & 0xFFFFFFFFFF000000) ||
> +	    ((res.a1 & 0xFF0000) >> 16) < 0x1) {
> +		pr_warn("%s: Invalid version (0x%016lx)\n",
> +			__func__, res.a1);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static int __init kvm_async_pf_info(void)
> +{
> +	struct arm_smccc_res res;
> +
> +	/* Retrieve number of tokens */
> +	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_ASYNC_PF_FUNC_ID,
> +			     ARM_SMCCC_KVM_FUNC_ASYNC_PF_SLOTS, &res);
> +	if (res.a0 != SMCCC_RET_SUCCESS) {
> +		pr_warn("%s: Error %ld to get token number\n",
> +			__func__, res.a0);
> +		return -EPERM;
> +	}
> +
> +	apf_tasks = res.a1 * 2;
> +
> +	/* Retrieve SDEI event number */
> +	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_ASYNC_PF_FUNC_ID,
> +			     ARM_SMCCC_KVM_FUNC_ASYNC_PF_SDEI, &res);
> +	if (res.a0 != SMCCC_RET_SUCCESS) {
> +		pr_warn("%s: Error %ld to get SDEI event number\n",
> +			__func__, res.a0);
> +		return -EPERM;
> +	}
> +
> +	apf_sdei_num = res.a1;
> +
> +	/* Retrieve (PPI) interrupt number */
> +	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_ASYNC_PF_FUNC_ID,
> +			     ARM_SMCCC_KVM_FUNC_ASYNC_PF_IRQ, &res);
> +	if (res.a0 != SMCCC_RET_SUCCESS) {
> +		pr_warn("%s: Error %ld to get IRQ\n",
> +			__func__, res.a0);
> +		return -EPERM;
> +	}
> +
> +	apf_ppi_num = res.a1;
> +
> +	return 0;
> +}
> +
> +static int __init kvm_async_pf_init(void)
> +{
> +	struct kvm_apf_table *table;
> +	size_t size;
> +	int cpu, i, ret;
> +
> +	if (!kvm_para_has_feature(KVM_FEATURE_ASYNC_PF) ||
> +	    !async_pf_available)
> +		return -EPERM;
> +
> +	ret = kvm_async_pf_check_version();
> +	if (ret)
> +		return ret;
> +
> +	ret = kvm_async_pf_info();
> +	if (ret)
> +		return ret;
> +
> +	/* Allocate and initialize the sleeper table */
> +	size = sizeof(struct kvm_apf_table) +
> +	       apf_tasks * sizeof(struct kvm_apf_task);
> +	apf_tables = __alloc_percpu(size, 0);
> +	if (!apf_tables) {
> +		pr_warn("%s: Unable to alloc async PF table\n",
> +			__func__);
> +		return -ENOMEM;
> +	}
> +
> +	for_each_possible_cpu(cpu) {
> +		table = per_cpu_ptr(apf_tables, cpu);
> +		raw_spin_lock_init(&table->lock);
> +		for (i = 0; i < apf_tasks; i++)
> +			init_swait_queue_head(&table->tasks[i].wq);
> +	}
> +
> +	/*
> +	 * Initialize SDEI event for page-not-present notification.
> +	 * The SDEI event number should have been retrieved from
> +	 * the host.
> +	 */
> +	ret = sdei_event_register(apf_sdei_num,
> +				  kvm_async_pf_sdei_handler, NULL);
> +	if (ret) {
> +		pr_warn("%s: Error %d to register SDEI event\n",
> +			__func__, ret);
> +		ret = -EIO;
> +		goto release_tables;
> +	}
> +
> +	ret = sdei_event_enable(apf_sdei_num);
> +	if (ret) {
> +		pr_warn("%s: Error %d to enable SDEI event\n",
> +			__func__, ret);
> +		goto unregister_event;
> +	}
> +
> +	/*
> +	 * Initialize interrupt for page-ready notification. The
> +	 * interrupt number and its properties should have been
> +	 * retrieved from the ACPI:APFT table.
> +	 */
> +	apf_irq = acpi_register_gsi(NULL, apf_ppi_num,
> +				    ACPI_LEVEL_SENSITIVE, ACPI_ACTIVE_HIGH);
> +	if (apf_irq <= 0) {
> +		ret = -EIO;
> +		pr_warn("%s: Error %d to register IRQ\n",
> +			__func__, apf_irq);
> +		goto disable_event;
> +	}
> +
> +	ret = request_percpu_irq(apf_irq, kvm_async_pf_irq_handler,
> +				 "Asynchronous Page Fault", &apf_data);
> +	if (ret) {
> +		pr_warn("%s: Error %d to request IRQ\n",
> +			__func__, ret);
> +		goto unregister_irq;
> +	}
> +
> +	register_reboot_notifier(&kvm_async_pf_cpu_reboot_nb);
> +	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> +			"arm/kvm:online", kvm_async_pf_cpu_online,
> +			kvm_async_pf_cpu_offline);
> +	if (ret < 0) {
> +		pr_warn("%s: Error %d to install cpu hotplug callbacks\n",
> +			__func__, ret);
> +		goto release_irq;
> +	}
> +
> +	/* Enable async PF on the online CPUs */
> +	on_each_cpu(kvm_async_pf_cpu_enable, NULL, 1);
> +
> +	return 0;
> +
> +release_irq:
> +	free_percpu_irq(apf_irq, &apf_data);
> +unregister_irq:
> +	acpi_unregister_gsi(apf_ppi_num);
> +disable_event:
> +	sdei_event_disable(apf_sdei_num);
> +unregister_event:
> +	sdei_event_unregister(apf_sdei_num);
> +release_tables:
> +	free_percpu(apf_tables);
> +
> +	return ret;
> +}
> +
> +static int __init kvm_guest_init(void)
> +{
> +	return kvm_async_pf_init();
> +}
> +
> +fs_initcall(kvm_guest_init);

-- 
Vitaly