linux-kernel - Re: [PING PATCH v4 23/29] LoongArch: KVM: Implement handle gspr exception

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Message-ID: <7463da3b-1d52-40a4-97a3-4f912f4f9fdb@redhat.com>
Date:   Tue, 28 Mar 2023 16:13:54 +0200
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,
        Xi Ruoyao <xry111@...111.site>
Subject: Re: [PING PATCH v4 23/29] LoongArch: KVM: Implement handle gspr
 exception

On 3/28/23 14:31, Tianrui Zhao wrote:
> +			case 0xc91:
> +				/* idle GSPR */
> +				er = _kvm_emu_idle(vcpu);
> +				break;

So this is my last remark.  What some other architectures do is change 
vcpu->arch.mp_state when entering an idle state, and at this point all 
calls to KVM_RUN would call the equivalent of _kvm_emu_idle().  This 
requires implementing the KVM_GET_MPSTATE and KVM_SET_MPSTATE ioctls.

This might also be useful if later you want to implement a mechanism 
where vCPUs can pause or resume, for example for multi-vCPU VMs.

You can implement this on top of what you have, but I highly recommend 
that you do it in the first version of what is committed to Linux.

Paolo