linux-kernel - Re: [PATCH] LoongArch: KVM: Access mailbox directly in mail

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Message-ID: <3fdcce8e-dff6-4871-82b3-571144a26c51@linux.dev>
Date: Thu, 31 Jul 2025 17:30:32 +0800
From: Yanteng Si <si.yanteng@...ux.dev>
To: Bibo Mao <maobibo@...ngson.cn>, Tianrui Zhao <zhaotianrui@...ngson.cn>,
 Huacai Chen <chenhuacai@...nel.org>, Xianglai Li <lixianglai@...ngson.cn>
Cc: kvm@...r.kernel.org, loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: KVM: Access mailbox directly in mail_send()

在 7/31/25 3:59 PM, Bibo Mao 写道:
> With function mail_send(), it is to write mailbox of other VCPUs.
> Existing simple APIs read_mailbox/write_mailbox can be used directly
> rather than send command on IOCSR address.
Hmm, that's indeed a feasible approach. However, I'm
curious: what is the purpose of designing IOCSR in
LoongArch? Is it merely to make things "complicated"?

Thanks,
Yanteng
> 
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
>   arch/loongarch/kvm/intc/ipi.c | 16 +++++++++++++---
>   1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/loongarch/kvm/intc/ipi.c b/arch/loongarch/kvm/intc/ipi.c
> index fe734dc062ed..832b2d4aa2ef 100644
> --- a/arch/loongarch/kvm/intc/ipi.c
> +++ b/arch/loongarch/kvm/intc/ipi.c
> @@ -134,7 +134,8 @@ static int send_ipi_data(struct kvm_vcpu *vcpu, gpa_t addr, uint64_t data)
>   
>   static int mail_send(struct kvm *kvm, uint64_t data)
>   {
> -	int cpu, mailbox, offset;
> +	int i, cpu, mailbox, offset;
> +	uint32_t val = 0, mask = 0;
>   	struct kvm_vcpu *vcpu;
>   
>   	cpu = ((data & 0xffffffff) >> 16) & 0x3ff;
> @@ -144,9 +145,18 @@ static int mail_send(struct kvm *kvm, uint64_t data)
>   		return -EINVAL;
>   	}
>   	mailbox = ((data & 0xffffffff) >> 2) & 0x7;
> -	offset = IOCSR_IPI_BASE + IOCSR_IPI_BUF_20 + mailbox * 4;
> +	offset = IOCSR_IPI_BUF_20 + mailbox * 4;
> +	if ((data >> 27) & 0xf) {
> +		val = read_mailbox(vcpu, offset, 4);
> +		for (i = 0; i < 4; i++)
> +			if (data & (BIT(27 + i)))
> +				mask |= (0xff << (i * 8));
> +		val &= mask;
> +	}
>   
> -	return send_ipi_data(vcpu, offset, data);
> +	val |= ((uint32_t)(data >> 32) & ~mask);
> +	write_mailbox(vcpu, offset, val, 4);
> +	return 0;
>   }
>   
>   static int any_send(struct kvm *kvm, uint64_t data)
> 
> base-commit: 038d61fd642278bab63ee8ef722c50d10ab01e8f