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Subject: Re: [PATCH v7 7/7] Documentation: KVM: Add hypercall for LoongArch
To: WANG Xuerui <kernel@xen0n.name>, Huacai Chen <chenhuacai@kernel.org>,
 Tianrui Zhao <zhaotianrui@loongson.cn>, Juergen Gross <jgross@suse.com>,
 Paolo Bonzini <pbonzini@redhat.com>, Jonathan Corbet <corbet@lwn.net>
Cc: loongarch@lists.linux.dev, linux-kernel@vger.kernel.org,
 virtualization@lists.linux.dev, kvm@vger.kernel.org
References: <20240315080710.2812974-1-maobibo@loongson.cn>
 <20240315081104.2813031-1-maobibo@loongson.cn>
 <68473508-dbf1-4875-a392-88ca09f7ea63@xen0n.name>
From: maobibo <maobibo@loongson.cn>
Message-ID: <0bdcaf41-c54d-9f39-0dd2-3b3d2a954649@loongson.cn>
Date: Tue, 2 Apr 2024 09:15:51 +0800
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On 2024/3/24 上午2:40, WANG Xuerui wrote:
> On 3/15/24 16:11, Bibo Mao wrote:
>> [snip]
>> +KVM hypercall ABI
>> +=================
>> +
>> +Hypercall ABI on KVM is simple, only one scratch register a0 and at most
>> +five generic registers used as input parameter. FP register and 
>> vector register
>> +is not used for input register and should not be modified during 
>> hypercall.
>> +Hypercall function can be inlined since there is only one scratch 
>> register.
> 
> Maybe it's better to describe the list of preserved registers with an 
> expression such as "all non-GPR registers shall remain unmodified after 
> returning from the hypercall", to guard ourselves against future ISA 
> state additions.
Sorry, I do not understand. What is the meaning of "all non-GPR 
registers"?  Can you give an example?

Regards
Bibo Mao
> 
> But I still maintain that it's better to promise less here, and only 
> hint on the extensive preservation of context as an implementation 
> detail. It is for not losing our ability to save/restore less in the 
> future, should we decide to do so.
>