Re: [RFC PATCH v2 1/5] pvsched: paravirt scheduling framework

[Vineeth Remanan Pillai]

Adding sched_ext folks

On Wed, Apr 3, 2024 at 10:01 AM Vineeth Pillai (Google)
<vineeth@xxxxxxxxxxxxxxx> wrote:
>
> Implement a paravirt scheduling framework for linux kernel.
>
> The framework allows for pvsched driver to register to the kernel and
> receive callbacks from hypervisor(eg: kvm) for interested vcpu events
> like VMENTER, VMEXIT etc.
>
> The framework also allows hypervisor to select a pvsched driver (from
> the available list of registered drivers) for each guest.
>
> Also implement a sysctl for listing the available pvsched drivers.
>
> Signed-off-by: Vineeth Pillai (Google) <vineeth@xxxxxxxxxxxxxxx>
> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> ---
>  Kconfig                 |   2 +
>  include/linux/pvsched.h | 102 +++++++++++++++++++
>  kernel/sysctl.c         |  27 +++++
>  virt/Makefile           |   2 +-
>  virt/pvsched/Kconfig    |  12 +++
>  virt/pvsched/Makefile   |   2 +
>  virt/pvsched/pvsched.c  | 215 ++++++++++++++++++++++++++++++++++++++++
>  7 files changed, 361 insertions(+), 1 deletion(-)
>  create mode 100644 include/linux/pvsched.h
>  create mode 100644 virt/pvsched/Kconfig
>  create mode 100644 virt/pvsched/Makefile
>  create mode 100644 virt/pvsched/pvsched.c
>
> diff --git a/Kconfig b/Kconfig
> index 745bc773f567..4a52eaa21166 100644
> --- a/Kconfig
> +++ b/Kconfig
> @@ -29,4 +29,6 @@ source "lib/Kconfig"
>
>  source "lib/Kconfig.debug"
>
> +source "virt/pvsched/Kconfig"
> +
>  source "Documentation/Kconfig"
> diff --git a/include/linux/pvsched.h b/include/linux/pvsched.h
> new file mode 100644
> index 000000000000..59df6b44aacb
> --- /dev/null
> +++ b/include/linux/pvsched.h
> @@ -0,0 +1,102 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (c) 2024 Google  */
> +
> +#ifndef _LINUX_PVSCHED_H
> +#define _LINUX_PVSCHED_H 1
> +
> +/*
> + * List of events for which hypervisor calls back into pvsched driver.
> + * Driver can specify the events it is interested in.
> + */
> +enum pvsched_vcpu_events {
> +       PVSCHED_VCPU_VMENTER = 0x1,
> +       PVSCHED_VCPU_VMEXIT = 0x2,
> +       PVSCHED_VCPU_HALT = 0x4,
> +       PVSCHED_VCPU_INTR_INJ = 0x8,
> +};
> +
> +#define PVSCHED_NAME_MAX       32
> +#define PVSCHED_MAX            8
> +#define PVSCHED_DRV_BUF_MAX    (PVSCHED_NAME_MAX * PVSCHED_MAX + PVSCHED_MAX)
> +
> +/*
> + * pvsched driver callbacks.
> + * TODO: versioning support for better compatibility with the guest
> + *       component implementing this feature.
> + */
> +struct pvsched_vcpu_ops {
> +       /*
> +        * pvsched_vcpu_register() - Register the vcpu with pvsched driver.
> +        * @pid: pid of the vcpu task.
> +        *
> +        * pvsched driver can store the pid internally and initialize
> +        * itself to prepare for receiving callbacks from thsi vcpu.
> +        */
> +       int (*pvsched_vcpu_register)(struct pid *pid);
> +
> +       /*
> +        * pvsched_vcpu_unregister() - Un-register the vcpu with pvsched driver.
> +        * @pid: pid of the vcpu task.
> +        */
> +       void (*pvsched_vcpu_unregister)(struct pid *pid);
> +
> +       /*
> +        * pvsched_vcpu_notify_event() - Callback for pvsched events
> +        * @addr: Address of the memory region shared with guest
> +        * @pid: pid of the vcpu task.
> +        * @events: bit mask of the events that hypervisor wants to notify.
> +        */
> +       void (*pvsched_vcpu_notify_event)(void *addr, struct pid *pid, u32 event);
> +
> +       char name[PVSCHED_NAME_MAX];
> +       struct module *owner;
> +       struct list_head list;
> +       u32 events;
> +       u32 key;
> +};
> +
> +#ifdef CONFIG_PARAVIRT_SCHED_HOST
> +int pvsched_get_available_drivers(char *buf, size_t maxlen);
> +
> +int pvsched_register_vcpu_ops(struct pvsched_vcpu_ops *ops);
> +void pvsched_unregister_vcpu_ops(struct pvsched_vcpu_ops *ops);
> +
> +struct pvsched_vcpu_ops *pvsched_get_vcpu_ops(char *name);
> +void pvsched_put_vcpu_ops(struct pvsched_vcpu_ops *ops);
> +
> +static inline int pvsched_validate_vcpu_ops(struct pvsched_vcpu_ops *ops)
> +{
> +       /*
> +        * All callbacks are mandatory.
> +        */
> +       if (!ops->pvsched_vcpu_register || !ops->pvsched_vcpu_unregister ||
> +                       !ops->pvsched_vcpu_notify_event)
> +               return -EINVAL;
> +
> +       return 0;
> +}
> +#else
> +static inline void pvsched_get_available_drivers(char *buf, size_t maxlen)
> +{
> +}
> +
> +static inline int pvsched_register_vcpu_ops(struct pvsched_vcpu_ops *ops)
> +{
> +       return -ENOTSUPP;
> +}
> +
> +static inline void pvsched_unregister_vcpu_ops(struct pvsched_vcpu_ops *ops)
> +{
> +}
> +
> +static inline struct pvsched_vcpu_ops *pvsched_get_vcpu_ops(char *name)
> +{
> +       return NULL;
> +}
> +
> +static inline void pvsched_put_vcpu_ops(struct pvsched_vcpu_ops *ops)
> +{
> +}
> +#endif
> +
> +#endif
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 157f7ce2942d..10a18a791b4f 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -63,6 +63,7 @@
>  #include <linux/mount.h>
>  #include <linux/userfaultfd_k.h>
>  #include <linux/pid.h>
> +#include <linux/pvsched.h>
>
>  #include "../lib/kstrtox.h"
>
> @@ -1615,6 +1616,24 @@ int proc_do_static_key(struct ctl_table *table, int write,
>         return ret;
>  }
>
> +#ifdef CONFIG_PARAVIRT_SCHED_HOST
> +static int proc_pvsched_available_drivers(struct ctl_table *ctl,
> +                                                int write, void *buffer,
> +                                                size_t *lenp, loff_t *ppos)
> +{
> +       struct ctl_table tbl = { .maxlen = PVSCHED_DRV_BUF_MAX, };
> +       int ret;
> +
> +       tbl.data = kmalloc(tbl.maxlen, GFP_USER);
> +       if (!tbl.data)
> +               return -ENOMEM;
> +       pvsched_get_available_drivers(tbl.data, PVSCHED_DRV_BUF_MAX);
> +       ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
> +       kfree(tbl.data);
> +       return ret;
> +}
> +#endif
> +
>  static struct ctl_table kern_table[] = {
>         {
>                 .procname       = "panic",
> @@ -2033,6 +2052,14 @@ static struct ctl_table kern_table[] = {
>                 .extra1         = SYSCTL_ONE,
>                 .extra2         = SYSCTL_INT_MAX,
>         },
> +#endif
> +#ifdef CONFIG_PARAVIRT_SCHED_HOST
> +       {
> +               .procname       = "pvsched_available_drivers",
> +               .maxlen         = PVSCHED_DRV_BUF_MAX,
> +               .mode           = 0444,
> +               .proc_handler   = proc_pvsched_available_drivers,
> +       },
>  #endif
>         { }
>  };
> diff --git a/virt/Makefile b/virt/Makefile
> index 1cfea9436af9..9d0f32d775a1 100644
> --- a/virt/Makefile
> +++ b/virt/Makefile
> @@ -1,2 +1,2 @@
>  # SPDX-License-Identifier: GPL-2.0-only
> -obj-y  += lib/
> +obj-y  += lib/ pvsched/
> diff --git a/virt/pvsched/Kconfig b/virt/pvsched/Kconfig
> new file mode 100644
> index 000000000000..5ca2669060cb
> --- /dev/null
> +++ b/virt/pvsched/Kconfig
> @@ -0,0 +1,12 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +config PARAVIRT_SCHED_HOST
> +       bool "Paravirt scheduling framework in the host kernel"
> +       default n
> +       help
> +         Paravirtualized scheduling facilitates the exchange of scheduling
> +         related information between the host and guest through shared memory,
> +         enhancing the efficiency of vCPU thread scheduling by the hypervisor.
> +         An illustrative use case involves dynamically boosting the priority of
> +         a vCPU thread when the guest is executing a latency-sensitive workload
> +         on that specific vCPU.
> +         This config enables paravirt scheduling framework in the host kernel.
> diff --git a/virt/pvsched/Makefile b/virt/pvsched/Makefile
> new file mode 100644
> index 000000000000..4ca38e30479b
> --- /dev/null
> +++ b/virt/pvsched/Makefile
> @@ -0,0 +1,2 @@
> +
> +obj-$(CONFIG_PARAVIRT_SCHED_HOST) += pvsched.o
> diff --git a/virt/pvsched/pvsched.c b/virt/pvsched/pvsched.c
> new file mode 100644
> index 000000000000..610c85cf90d2
> --- /dev/null
> +++ b/virt/pvsched/pvsched.c
> @@ -0,0 +1,215 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright (c) 2024 Google  */
> +
> +/*
> + *  Paravirt scheduling framework
> + *
> + */
> +
> +/*
> + * Heavily inspired from tcp congestion avoidance implementation.
> + * (net/ipv4/tcp_cong.c)
> + */
> +
> +#define pr_fmt(fmt) "PVSCHED: " fmt
> +
> +#include <linux/module.h>
> +#include <linux/bpf.h>
> +#include <linux/gfp.h>
> +#include <linux/types.h>
> +#include <linux/list.h>
> +#include <linux/jhash.h>
> +#include <linux/pvsched.h>
> +
> +static DEFINE_SPINLOCK(pvsched_drv_list_lock);
> +static int nr_pvsched_drivers = 0;
> +static LIST_HEAD(pvsched_drv_list);
> +
> +/*
> + * Retrieve pvsched_vcpu_ops given the name.
> + */
> +static struct pvsched_vcpu_ops *pvsched_find_vcpu_ops_name(char *name)
> +{
> +       struct pvsched_vcpu_ops *ops;
> +
> +       list_for_each_entry_rcu(ops, &pvsched_drv_list, list) {
> +               if (strcmp(ops->name, name) == 0)
> +                       return ops;
> +       }
> +
> +       return NULL;
> +}
> +
> +/*
> + * Retrieve pvsched_vcpu_ops given the hash key.
> + */
> +static struct pvsched_vcpu_ops *pvsched_find_vcpu_ops_key(u32 key)
> +{
> +       struct pvsched_vcpu_ops *ops;
> +
> +       list_for_each_entry_rcu(ops, &pvsched_drv_list, list) {
> +               if (ops->key == key)
> +                       return ops;
> +       }
> +
> +       return NULL;
> +}
> +
> +/*
> + * pvsched_get_available_drivers() - Copy space separated list of pvsched
> + * driver names.
> + * @buf: buffer to store the list of driver names
> + * @maxlen: size of the buffer
> + *
> + * Return: 0 on success, negative value on error.
> + */
> +int pvsched_get_available_drivers(char *buf, size_t maxlen)
> +{
> +       struct pvsched_vcpu_ops *ops;
> +       size_t offs = 0;
> +
> +       if (!buf)
> +               return -EINVAL;
> +
> +       if (maxlen > PVSCHED_DRV_BUF_MAX)
> +               maxlen = PVSCHED_DRV_BUF_MAX;
> +
> +       rcu_read_lock();
> +       list_for_each_entry_rcu(ops, &pvsched_drv_list, list) {
> +               offs += snprintf(buf + offs, maxlen - offs,
> +                                "%s%s",
> +                                offs == 0 ? "" : " ", ops->name);
> +
> +               if (WARN_ON_ONCE(offs >= maxlen))
> +                       break;
> +       }
> +       rcu_read_unlock();
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(pvsched_get_available_drivers);
> +
> +/*
> + * pvsched_register_vcpu_ops() - Register the driver in the kernel.
> + * @ops: Driver data(callbacks)
> + *
> + * After the registration, driver will be exposed to the hypervisor
> + * for assignment to the guest VMs.
> + *
> + * Return: 0 on success, negative value on error.
> + */
> +int pvsched_register_vcpu_ops(struct pvsched_vcpu_ops *ops)
> +{
> +       int ret = 0;
> +
> +       ops->key = jhash(ops->name, sizeof(ops->name), strlen(ops->name));
> +       spin_lock(&pvsched_drv_list_lock);
> +       if (nr_pvsched_drivers > PVSCHED_MAX) {
> +               ret = -ENOSPC;
> +       } if (pvsched_find_vcpu_ops_key(ops->key)) {
> +               ret = -EEXIST;
> +       } else if (!(ret = pvsched_validate_vcpu_ops(ops))) {
> +               list_add_tail_rcu(&ops->list, &pvsched_drv_list);
> +               nr_pvsched_drivers++;
> +       }
> +       spin_unlock(&pvsched_drv_list_lock);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(pvsched_register_vcpu_ops);
> +
> +/*
> + * pvsched_register_vcpu_ops() - Un-register the driver from the kernel.
> + * @ops: Driver data(callbacks)
> + *
> + * After un-registration, driver will not be visible to hypervisor.
> + */
> +void pvsched_unregister_vcpu_ops(struct pvsched_vcpu_ops *ops)
> +{
> +       spin_lock(&pvsched_drv_list_lock);
> +       list_del_rcu(&ops->list);
> +       nr_pvsched_drivers--;
> +       spin_unlock(&pvsched_drv_list_lock);
> +
> +       synchronize_rcu();
> +}
> +EXPORT_SYMBOL_GPL(pvsched_unregister_vcpu_ops);
> +
> +/*
> + * pvsched_get_vcpu_ops: Acquire the driver.
> + * @name: Name of the driver to be acquired.
> + *
> + * Hypervisor can use this API to get the driver structure for
> + * assigning it to guest VMs. This API takes a reference on the
> + * module/bpf program so that driver doesn't vanish under the
> + * hypervisor.
> + *
> + * Return: driver structure if found, else NULL.
> + */
> +struct pvsched_vcpu_ops *pvsched_get_vcpu_ops(char *name)
> +{
> +       struct pvsched_vcpu_ops *ops;
> +
> +       if (!name || (strlen(name) >= PVSCHED_NAME_MAX))
> +               return NULL;
> +
> +       rcu_read_lock();
> +       ops = pvsched_find_vcpu_ops_name(name);
> +       if (!ops)
> +               goto out;
> +
> +       if (unlikely(!bpf_try_module_get(ops, ops->owner))) {
> +               ops = NULL;
> +               goto out;
> +       }
> +
> +out:
> +       rcu_read_unlock();
> +       return ops;
> +}
> +EXPORT_SYMBOL_GPL(pvsched_get_vcpu_ops);
> +
> +/*
> + * pvsched_put_vcpu_ops: Release the driver.
> + * @name: Name of the driver to be releases.
> + *
> + * Hypervisor can use this API to release the driver.
> + */
> +void pvsched_put_vcpu_ops(struct pvsched_vcpu_ops *ops)
> +{
> +       bpf_module_put(ops, ops->owner);
> +}
> +EXPORT_SYMBOL_GPL(pvsched_put_vcpu_ops);
> +
> +/*
> + * NOP vm_ops Sample implementation.
> + * This driver doesn't do anything other than registering itself.
> + * Placeholder for adding some default logic when the feature is
> + * complete.
> + */
> +static int nop_pvsched_vcpu_register(struct pid *pid)
> +{
> +       return 0;
> +}
> +static void nop_pvsched_vcpu_unregister(struct pid *pid)
> +{
> +}
> +static void nop_pvsched_notify_event(void *addr, struct pid *pid, u32 event)
> +{
> +}
> +
> +struct pvsched_vcpu_ops nop_vcpu_ops = {
> +       .events = PVSCHED_VCPU_VMENTER | PVSCHED_VCPU_VMEXIT | PVSCHED_VCPU_HALT,
> +       .pvsched_vcpu_register = nop_pvsched_vcpu_register,
> +       .pvsched_vcpu_unregister = nop_pvsched_vcpu_unregister,
> +       .pvsched_vcpu_notify_event = nop_pvsched_notify_event,
> +       .name = "pvsched_nop",
> +       .owner = THIS_MODULE,
> +};
> +
> +static int __init pvsched_init(void)
> +{
> +       return WARN_ON(pvsched_register_vcpu_ops(&nop_vcpu_ops));
> +}
> +
> +late_initcall(pvsched_init);
> --
> 2.40.1
>