linux-kernel - Re: [PATCH 3/4] KVM: X86: Refactor kvm_arch_vcpu

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Message-ID: <20191017161221.GB20903@linux.intel.com>
Date:   Thu, 17 Oct 2019 09:12:21 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] KVM: X86: Refactor kvm_arch_vcpu_create

On Wed, Oct 16, 2019 at 12:40:32AM +0800, Xiaoyao Li wrote:
> Current x86 arch vcpu creation flow is a little bit messed.
> Specifically, vcpu's data structure allocation and vcpu initialization
> are mixed up, which is unfriendly to read.
> 
> Seperating the vcpu_create and vcpu_init just like what ARM does, that
> it first calls vcpu_create related functions for vcpu's data structure
> allocation and then calls vcpu_init related functions to initialize the
> vcpu.

My vote is to take advantage of the requirement that @vcpu must reside at
offset 0 in vmx_vcpu and svm_vcpu, and allocate the vcpu in x86 code.
That would allow kvm_arch_vcpu_create() to invoke kvm_vcpu_init() directly
instead of bouncing through the vendor code.

And if we're extra lucky and the other architectures can use a similar
pattern, kvm_vm_ioctl_create_vcpu() could be refactored to something like:

	vcpu = kvm_arch_vcpu_alloc(kvm, id);
	if (IS_ERR(vcpu)) {
		r = PTR_ERR(vcpu);
		goto vcpu_decrement;
	}

	r = kvm_arch_vcpu_init(vcpu);
	if (r)
		goto vcpu_destroy;