linux-kernel - Re: [PATCH v4 2/2] LoongArch: Add paravirt support with vcpu_is

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Message-ID: <CAAhV-H7N1uXzK6Fu4x4Mrq4j1P95119HP87_spxU_E6WLxN6TQ@mail.gmail.com>
Date: Thu, 29 Jan 2026 20:55:13 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: Juergen Gross <jgross@...e.com>, Tianrui Zhao <zhaotianrui@...ngson.cn>, 
	WANG Xuerui <kernel@...0n.name>, kvm@...r.kernel.org, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] LoongArch: Add paravirt support with
 vcpu_is_preempted() in guest side

Hi, Bibo,

On Fri, Dec 19, 2025 at 2:30 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>
> Function vcpu_is_preempted() is used to check whether vCPU is preempted
> or not. Here add implementation with vcpu_is_preempted() when option
> CONFIG_PARAVIRT is enabled.
>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> Acked-by: Juergen Gross <jgross@...e.com>
> ---
>  arch/loongarch/include/asm/qspinlock.h |  3 +++
>  arch/loongarch/kernel/paravirt.c       | 21 ++++++++++++++++++++-
>  2 files changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/include/asm/qspinlock.h b/arch/loongarch/include/asm/qspinlock.h
> index e76d3aa1e1eb..fa3eaf7e48f2 100644
> --- a/arch/loongarch/include/asm/qspinlock.h
> +++ b/arch/loongarch/include/asm/qspinlock.h
> @@ -34,6 +34,9 @@ static inline bool virt_spin_lock(struct qspinlock *lock)
>         return true;
>  }
>
> +#define vcpu_is_preempted      vcpu_is_preempted
> +bool vcpu_is_preempted(int cpu);
> +
>  #endif /* CONFIG_PARAVIRT */
>
>  #include <asm-generic/qspinlock.h>
> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
> index b1b51f920b23..a81a3e871dd1 100644
> --- a/arch/loongarch/kernel/paravirt.c
> +++ b/arch/loongarch/kernel/paravirt.c
> @@ -12,6 +12,7 @@ static int has_steal_clock;
>  struct static_key paravirt_steal_enabled;
>  struct static_key paravirt_steal_rq_enabled;
>  static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
> +static DEFINE_STATIC_KEY_FALSE(virt_preempt_key);
>  DEFINE_STATIC_KEY_FALSE(virt_spin_lock_key);
>
>  static u64 native_steal_clock(int cpu)
> @@ -267,6 +268,18 @@ static int pv_time_cpu_down_prepare(unsigned int cpu)
>
>         return 0;
>  }
> +
> +bool notrace vcpu_is_preempted(int cpu)
Is "notrace" really needed? Only S390 do this.

Huacai

> +{
> +       struct kvm_steal_time *src;
> +
> +       if (!static_branch_unlikely(&virt_preempt_key))
> +               return false;
> +
> +       src = &per_cpu(steal_time, cpu);
> +       return !!(src->preempted & KVM_VCPU_PREEMPTED);
> +}
> +EXPORT_SYMBOL(vcpu_is_preempted);
>  #endif
>
>  static void pv_cpu_reboot(void *unused)
> @@ -308,6 +321,9 @@ int __init pv_time_init(void)
>                 pr_err("Failed to install cpu hotplug callbacks\n");
>                 return r;
>         }
> +
> +       if (kvm_para_has_feature(KVM_FEATURE_PREEMPT))
> +               static_branch_enable(&virt_preempt_key);
>  #endif
>
>         static_call_update(pv_steal_clock, paravt_steal_clock);
> @@ -318,7 +334,10 @@ int __init pv_time_init(void)
>                 static_key_slow_inc(&paravirt_steal_rq_enabled);
>  #endif
>
> -       pr_info("Using paravirt steal-time\n");
> +       if (static_key_enabled(&virt_preempt_key))
> +               pr_info("Using paravirt steal-time with preempt enabled\n");
> +       else
> +               pr_info("Using paravirt steal-time with preempt disabled\n");
>
>         return 0;
>  }
> --
> 2.39.3
>