linux-kernel - Re: [PATCH 1/2] LoongArch: KVM: rework kvm_send_pv

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Message-ID: <a70dba22-c18e-3b28-6d2e-1eb7a4688a1d@loongson.cn>
Date: Fri, 18 Jul 2025 10:25:43 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Yury Norov <yury.norov@...il.com>, Tianrui Zhao
 <zhaotianrui@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>,
 WANG Xuerui <kernel@...0n.name>, kvm@...r.kernel.org,
 loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] LoongArch: KVM: rework kvm_send_pv_ipi()



On 2025/7/17 上午12:59, Yury Norov wrote:
> From: "Yury Norov (NVIDIA)" <yury.norov@...il.com>
> 
> The function in fact traverses a "bitmap" stored in GPR regs A1 and A2,
> but does it in a non-obvious way by creating a single-word bitmap twice.
> 
> This patch switches the function to create a single 2-word bitmap, and
> also employs for_each_set_bit() macro, as it helps to drop most of
> housekeeping code.
> 
> While there, convert the function to return void to not confuse readers
> with unchecked result.
> 
> Signed-off-by: Yury Norov (NVIDIA) <yury.norov@...il.com>
> ---
>   arch/loongarch/kvm/exit.c | 31 ++++++++++++-------------------
>   1 file changed, 12 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
> index fa52251b3bf1..359afa909cee 100644
> --- a/arch/loongarch/kvm/exit.c
> +++ b/arch/loongarch/kvm/exit.c
> @@ -821,32 +821,25 @@ static int kvm_handle_lbt_disabled(struct kvm_vcpu *vcpu, int ecode)
>   	return RESUME_GUEST;
>   }
>   
> -static int kvm_send_pv_ipi(struct kvm_vcpu *vcpu)
> +static void kvm_send_pv_ipi(struct kvm_vcpu *vcpu)
>   {
> -	unsigned int min, cpu, i;
> -	unsigned long ipi_bitmap;
> +	DECLARE_BITMAP(ipi_bitmap, BITS_PER_LONG * 2) = {
> +		kvm_read_reg(vcpu, LOONGARCH_GPR_A1),
> +		kvm_read_reg(vcpu, LOONGARCH_GPR_A2)
> +	};
> +	unsigned int min, cpu;
>   	struct kvm_vcpu *dest;
>   
>   	min = kvm_read_reg(vcpu, LOONGARCH_GPR_A3);
> -	for (i = 0; i < 2; i++, min += BITS_PER_LONG) {
> -		ipi_bitmap = kvm_read_reg(vcpu, LOONGARCH_GPR_A1 + i);
> -		if (!ipi_bitmap)
> +	for_each_set_bit(cpu, ipi_bitmap, BITS_PER_LONG * 2) {
> +		dest = kvm_get_vcpu_by_cpuid(vcpu->kvm, cpu + min);
> +		if (!dest)
>   			continue;
>   
> -		cpu = find_first_bit((void *)&ipi_bitmap, BITS_PER_LONG);
> -		while (cpu < BITS_PER_LONG) {
> -			dest = kvm_get_vcpu_by_cpuid(vcpu->kvm, cpu + min);
> -			cpu = find_next_bit((void *)&ipi_bitmap, BITS_PER_LONG, cpu + 1);
> -			if (!dest)
> -				continue;
> -
> -			/* Send SWI0 to dest vcpu to emulate IPI interrupt */
> -			kvm_queue_irq(dest, INT_SWI0);
> -			kvm_vcpu_kick(dest);
> -		}
> +		/* Send SWI0 to dest vcpu to emulate IPI interrupt */
> +		kvm_queue_irq(dest, INT_SWI0);
> +		kvm_vcpu_kick(dest);
>   	}
> -
> -	return 0;
>   }
>   
>   /*
> 
Reviewed-by: Bibo Mao <maobibo@...ngson.cn>