linux-kernel - Re: [PATCH v2 2/3] LoongArch: Add paravirt support with vcpu_is

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Message-ID: <CAAhV-H5Oag+mDp0CfZ1VDeapeKas354j68JZN9bN42=D4huowA@mail.gmail.com>
Date: Mon, 24 Nov 2025 14:33:10 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: Paolo Bonzini <pbonzini@...hat.com>, WANG Xuerui <kernel@...0n.name>, 
	Juergen Gross <jgross@...e.com>, Ajay Kaher <ajay.kaher@...adcom.com>, 
	Alexey Makhalov <alexey.makhalov@...adcom.com>, 
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, kvm@...r.kernel.org, 
	loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	virtualization@...ts.linux.dev, x86@...nel.org
Subject: Re: [PATCH v2 2/3] LoongArch: Add paravirt support with
 vcpu_is_preempted() in guest side

Hi, Bibo,

On Mon, Nov 24, 2025 at 11:54 AM 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>
> ---
>  arch/loongarch/include/asm/qspinlock.h |  5 +++++
>  arch/loongarch/kernel/paravirt.c       | 16 ++++++++++++++++
>  2 files changed, 21 insertions(+)
>
> diff --git a/arch/loongarch/include/asm/qspinlock.h b/arch/loongarch/include/asm/qspinlock.h
> index e76d3aa1e1eb..9a5b7ba1f4cb 100644
> --- a/arch/loongarch/include/asm/qspinlock.h
> +++ b/arch/loongarch/include/asm/qspinlock.h
> @@ -34,6 +34,11 @@ static inline bool virt_spin_lock(struct qspinlock *lock)
>         return true;
>  }
>
> +#ifdef CONFIG_SMP
> +#define vcpu_is_preempted      vcpu_is_preempted
> +bool vcpu_is_preempted(int cpu);
In V1 there is a build error because you reference mp_ops, so in V2
you needn't put it in CONFIG_SMP.
On the other hand, even if you really build a UP guest kernel, when
multiple guests run together, you probably need vcpu_is_preemtped.


Huacai

> +#endif
> +
>  #endif /* CONFIG_PARAVIRT */
>
>  #include <asm-generic/qspinlock.h>
> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
> index b1b51f920b23..d4163679adc4 100644
> --- a/arch/loongarch/kernel/paravirt.c
> +++ b/arch/loongarch/kernel/paravirt.c
> @@ -246,6 +246,7 @@ static void pv_disable_steal_time(void)
>  }
>
>  #ifdef CONFIG_SMP
> +DEFINE_STATIC_KEY_FALSE(virt_preempt_key);
>  static int pv_time_cpu_online(unsigned int cpu)
>  {
>         unsigned long flags;
> @@ -267,6 +268,18 @@ static int pv_time_cpu_down_prepare(unsigned int cpu)
>
>         return 0;
>  }
> +
> +bool notrace vcpu_is_preempted(int cpu)
> +{
> +       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);
> --
> 2.39.3
>