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SubjectRe: [PATCH v1] cpuidle-haltpoll: vcpu hotplug support
Hi Joao,

On Wed, Aug 28, 2019 at 07:56:50PM +0100, Joao Martins wrote:
> When cpus != maxcpus cpuidle-haltpoll will fail to register all vcpus
> past the online ones and thus fail to register the idle driver.
> This is because cpuidle_add_sysfs() will return with -ENODEV as a
> consequence from get_cpu_device() return no device for a non-existing
> CPU.
>
> Instead switch to cpuidle_register_driver() and manually register each
> of the present cpus through cpuhp_setup_state() and future ones that
> get onlined. This mimics similar logic as intel_idle.
>
> Fixes: fa86ee90eb11 ("add cpuidle-haltpoll driver")
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> ---
> arch/x86/include/asm/cpuidle_haltpoll.h | 4 +-
> arch/x86/kernel/kvm.c | 18 +++----
> drivers/cpuidle/cpuidle-haltpoll.c | 65 +++++++++++++++++++++++--
> include/linux/cpuidle_haltpoll.h | 4 +-
> 4 files changed, 70 insertions(+), 21 deletions(-)
>
> diff --git a/arch/x86/include/asm/cpuidle_haltpoll.h b/arch/x86/include/asm/cpuidle_haltpoll.h
> index ff8607d81526..c8b39c6716ff 100644
> --- a/arch/x86/include/asm/cpuidle_haltpoll.h
> +++ b/arch/x86/include/asm/cpuidle_haltpoll.h
> @@ -2,7 +2,7 @@
> #ifndef _ARCH_HALTPOLL_H
> #define _ARCH_HALTPOLL_H
>
> -void arch_haltpoll_enable(void);
> -void arch_haltpoll_disable(void);
> +void arch_haltpoll_enable(unsigned int cpu);
> +void arch_haltpoll_disable(unsigned int cpu);
>
> #endif
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 8d150e3732d9..a9b6c4e2446d 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -880,32 +880,26 @@ static void kvm_enable_host_haltpoll(void *i)
> wrmsrl(MSR_KVM_POLL_CONTROL, 1);
> }
>
> -void arch_haltpoll_enable(void)
> +void arch_haltpoll_enable(unsigned int cpu)
> {
> if (!kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL)) {
> - printk(KERN_ERR "kvm: host does not support poll control\n");
> - printk(KERN_ERR "kvm: host upgrade recommended\n");
> + pr_err_once("kvm: host does not support poll control\n");
> + pr_err_once("kvm: host upgrade recommended\n");
> return;
> }
>
> - preempt_disable();
> /* Enable guest halt poll disables host halt poll */
> - kvm_disable_host_haltpoll(NULL);
> - smp_call_function(kvm_disable_host_haltpoll, NULL, 1);
> - preempt_enable();
> + smp_call_function_single(cpu, kvm_disable_host_haltpoll, NULL, 1);
> }
> EXPORT_SYMBOL_GPL(arch_haltpoll_enable);
>
> -void arch_haltpoll_disable(void)
> +void arch_haltpoll_disable(unsigned int cpu)
> {
> if (!kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL))
> return;
>
> - preempt_disable();
> /* Enable guest halt poll disables host halt poll */
> - kvm_enable_host_haltpoll(NULL);
> - smp_call_function(kvm_enable_host_haltpoll, NULL, 1);
> - preempt_enable();
> + smp_call_function_single(cpu, kvm_enable_host_haltpoll, NULL, 1);
> }
> EXPORT_SYMBOL_GPL(arch_haltpoll_disable);
> #endif
> diff --git a/drivers/cpuidle/cpuidle-haltpoll.c b/drivers/cpuidle/cpuidle-haltpoll.c
> index 9ac093dcbb01..0d1853a7185e 100644
> --- a/drivers/cpuidle/cpuidle-haltpoll.c
> +++ b/drivers/cpuidle/cpuidle-haltpoll.c
> @@ -11,12 +11,15 @@
> */
>
> #include <linux/init.h>
> +#include <linux/cpu.h>
> #include <linux/cpuidle.h>
> #include <linux/module.h>
> #include <linux/sched/idle.h>
> #include <linux/kvm_para.h>
> #include <linux/cpuidle_haltpoll.h>
>
> +static struct cpuidle_device __percpu *haltpoll_cpuidle_devices;
> +
> static int default_enter_idle(struct cpuidle_device *dev,
> struct cpuidle_driver *drv, int index)
> {
> @@ -46,6 +49,48 @@ static struct cpuidle_driver haltpoll_driver = {
> .state_count = 2,
> };
>
> +static int haltpoll_cpu_online(unsigned int cpu)
> +{
> + struct cpuidle_device *dev;
> +
> + dev = per_cpu_ptr(haltpoll_cpuidle_devices, cpu);
> + if (!dev->registered) {
> + dev->cpu = cpu;
> + if (cpuidle_register_device(dev)) {
> + pr_notice("cpuidle_register_device %d failed!\n", cpu);
> + return -EIO;
> + }
> + arch_haltpoll_enable(cpu);
> + }
> +
> + return 0;
> +}
> +
> +static void haltpoll_uninit(void)
> +{
> + unsigned int cpu;
> +
> + cpus_read_lock();
> +
> + for_each_online_cpu(cpu) {
> + struct cpuidle_device *dev =
> + per_cpu_ptr(haltpoll_cpuidle_devices, cpu);
> +
> + if (!dev->registered)
> + continue;
> +
> + arch_haltpoll_disable(cpu);
> + cpuidle_unregister_device(dev);
> + }

1)

> +
> + cpuidle_unregister(&haltpoll_driver);

cpuidle_unregister_driver.

> + free_percpu(haltpoll_cpuidle_devices);
> + haltpoll_cpuidle_devices = NULL;
> +
> + cpus_read_unlock();

Any reason you can't cpus_read_unlock() at 1) ?

Looks good otherwise.

Thanks!

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