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

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Message-ID: <77814b6c-7a51-e130-5006-d27a172e69aa@loongson.cn>
Date: Wed, 19 Nov 2025 10:50:23 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
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()



On 2025/11/18 下午8:48, Huacai Chen wrote:
> 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?
how about put it in asm/qspinlock.h since it is included by header file 
asm/spinlock.h already?

> 
>> +
>>   #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
>>
>>