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

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Message-ID: <CAAhV-H4hoS0Wo3TS+FdikXMkb7qjWNFSPDoajQr0bzdeROJwGw@mail.gmail.com>
Date: Tue, 18 Nov 2025 20:48:41 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: Paolo Bonzini <pbonzini@...hat.com>, WANG Xuerui <kernel@...0n.name>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, 
	Boqun Feng <boqun.feng@...il.com>, Waiman Long <longman@...hat.com>, 
	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 2/3] LoongArch: Add paravirt support with vcpu_is_preempted()

Hi, Bibo,

On Tue, Nov 18, 2025 at 4:07 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>
> ---
>  arch/loongarch/include/asm/smp.h      |  1 +
>  arch/loongarch/include/asm/spinlock.h |  5 +++++
>  arch/loongarch/kernel/paravirt.c      | 16 ++++++++++++++++
>  arch/loongarch/kernel/smp.c           |  6 ++++++
>  4 files changed, 28 insertions(+)
>
> diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h
> index 3a47f52959a8..5b37f7bf2060 100644
> --- a/arch/loongarch/include/asm/smp.h
> +++ b/arch/loongarch/include/asm/smp.h
> @@ -18,6 +18,7 @@ struct smp_ops {
>         void (*init_ipi)(void);
>         void (*send_ipi_single)(int cpu, unsigned int action);
>         void (*send_ipi_mask)(const struct cpumask *mask, unsigned int action);
> +       bool (*vcpu_is_preempted)(int cpu);
>  };
>  extern struct smp_ops mp_ops;
>
> diff --git a/arch/loongarch/include/asm/spinlock.h b/arch/loongarch/include/asm/spinlock.h
> index 7cb3476999be..c001cef893aa 100644
> --- a/arch/loongarch/include/asm/spinlock.h
> +++ b/arch/loongarch/include/asm/spinlock.h
> @@ -5,6 +5,11 @@
>  #ifndef _ASM_SPINLOCK_H
>  #define _ASM_SPINLOCK_H
>
> +#ifdef CONFIG_PARAVIRT
> +#define vcpu_is_preempted      vcpu_is_preempted
> +bool vcpu_is_preempted(int cpu);
> +#endif
Maybe paravirt.h is a better place?

> +
>  #include <asm/processor.h>
>  #include <asm/qspinlock.h>
>  #include <asm/qrwlock.h>
> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
> index b1b51f920b23..b99404b6b13f 100644
> --- a/arch/loongarch/kernel/paravirt.c
> +++ b/arch/loongarch/kernel/paravirt.c
> @@ -52,6 +52,13 @@ static u64 paravt_steal_clock(int cpu)
>  #ifdef CONFIG_SMP
>  static struct smp_ops native_ops;
>
> +static bool pv_vcpu_is_preempted(int cpu)
> +{
> +       struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
> +
> +       return !!(src->preempted & KVM_VCPU_PREEMPTED);
> +}
> +
>  static void pv_send_ipi_single(int cpu, unsigned int action)
>  {
>         int min, old;
> @@ -308,6 +315,9 @@ 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_HINT))
> +               mp_ops.vcpu_is_preempted = pv_vcpu_is_preempted;
>  #endif
>
>         static_call_update(pv_steal_clock, paravt_steal_clock);
> @@ -332,3 +342,9 @@ int __init pv_spinlock_init(void)
>
>         return 0;
>  }
> +
> +bool notrace vcpu_is_preempted(int cpu)
> +{
> +       return mp_ops.vcpu_is_preempted(cpu);
> +}

We can simplify the whole patch like this, then we don't need to touch
smp.c, and we can merge Patch-2/3.

+bool notrace vcpu_is_preempted(int cpu)
+{
+  if (!kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT))
+     return false;
+ else {
+     struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
+     return !!(src->preempted & KVM_VCPU_PREEMPTED);
+ }
+}
Huacai

> +EXPORT_SYMBOL(vcpu_is_preempted);
> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
> index 46036d98da75..f04192fedf8d 100644
> --- a/arch/loongarch/kernel/smp.c
> +++ b/arch/loongarch/kernel/smp.c
> @@ -307,10 +307,16 @@ static void loongson_init_ipi(void)
>                 panic("IPI IRQ request failed\n");
>  }
>
> +static bool loongson_vcpu_is_preempted(int cpu)
> +{
> +       return false;
> +}
> +
>  struct smp_ops mp_ops = {
>         .init_ipi               = loongson_init_ipi,
>         .send_ipi_single        = loongson_send_ipi_single,
>         .send_ipi_mask          = loongson_send_ipi_mask,
> +       .vcpu_is_preempted      = loongson_vcpu_is_preempted,
>  };
>
>  static void __init fdt_smp_setup(void)
> --
> 2.39.3
>
>