linux-kernel - Re: [PATCH v2 06/29] LoongArch: KVM: Implement vcpu create and destroy interface

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Message-ID: <a9623c91-a28a-d91d-5311-fcfc4bd13247@redhat.com>
Date:   Wed, 22 Feb 2023 13:17:25 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tianrui Zhao <zhaotianrui@...ngson.cn>
Cc:     Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Mark Brown <broonie@...nel.org>,
        Alex Deucher <alexander.deucher@....com>,
        Oliver Upton <oliver.upton@...ux.dev>, maobibo@...ngson.cn
Subject: Re: [PATCH v2 06/29] LoongArch: KVM: Implement vcpu create and
 destroy interface

On 2/22/23 02:52, Tianrui Zhao wrote:
>>
>>> +    vcpu->arch.guest_eentry = (unsigned long)kvm_context->kvm_eentry;
>>> +    vcpu->arch.vcpu_run = kvm_context->kvm_enter_guest;
>>> +    vcpu->arch.handle_exit = _kvm_handle_exit;
>>
>> Here as well, whatever is constant must not be stored in struct 
>> kvm_arch_vcpu.
>>
>> Paolo
> 
> Thanks,  we use this in vcpu_arch because the vcpu_arch is used as 
> argument in switch.S' methods, we can quickly access the guest_eentry 
> and handle_exit by using the  KVM_ARCH_GEENTRY, KVM_ARCH_HANDLE_EXIT 
> offsets. If we change to global variable ,  we should relocate it in 
> switch.S and may lead  to lower accessing speed.

For guest_eentry and handle_exit this is correct so you can add a 
comment in kvm_host.h, like

	/* Pointers stored here for easy access from assembly code.  */

However, vcpu->arch.vcpu_run is not used in switch.S so there is no need 
to store it in struct kvm_arch_vcpu.  Since you're already going to move 
kvm_enter_guest out of kvm_context and into a global variable, please 
give it the right pointer-to-function type instead of using unsigned long.

Paolo