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

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Message-ID: <7dc95f48-80c9-4756-98e2-95851c9fc536@linux.dev>
Date: Fri, 1 Aug 2025 13:32:57 +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 7:24 PM, Bibo Mao 写道:
> 
> 
> On 2025/7/31 下午5:30, Yanteng Si wrote:
>> 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"?
> 
> I am not chip designer -:). MMIO address space is ok from my side, however I do not know how to solve multi-chip problem with MMIO method.

I have reviewed many manuals published on loongson.cn and found
that your chip engineers recommend using IOCSR. Although I don't
know the specific reason, I believe it must have solved some problems,
so let's continue to use IOCSR. see:

《龙芯 3D5000 处理器 寄存器使用手册》第10章

龙芯 3D5000 中支持两种不同的访问方式,一种是地址访问模式,另一种是为了支持处理器寄存器空间的直接指令访问.后面章节进行分别说明.推荐使用处理器 IOCSR 指令访问


Thanks,
Yanteng
> 
> Regards
> Bibo Mao
>>
>> 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
>>
>