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

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Message-ID: <6793e1a8-00f6-c653-3a8a-5943c0471bb1@loongson.cn>
Date: Thu, 31 Jul 2025 19:24:23 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Yanteng Si <si.yanteng@...ux.dev>, 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()



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.

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
>