linux-kernel - Re: [PATCH v2 6/7] KVM: X86: Move kvm_x86_ops.update_vcpu_model() into kvm_update_vcpu

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Date:   Thu, 2 Jul 2020 11:59:13 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 6/7] KVM: X86: Move kvm_x86_ops.update_vcpu_model()
 into kvm_update_vcpu_model()

On Tue, Jun 23, 2020 at 07:58:15PM +0800, Xiaoyao Li wrote:
> kvm_x86_ops.update_vcpu_model() is used to update vmx/svm vcpu settings
> based on updated CPUID settings. So it's supposed to be called after
> CPUIDs are fully updated, i.e., kvm_update_cpuid().
> 
> Move it in kvm_update_vcpu_model().

The changelog needs to provide an in-depth analysis of VMX and SVM to prove
that there are no existing dependencies in the ordering.  I've done the
analysis a few times over the past few years for a similar chage I carried
in my SGX code, but dropped that code a while back and haven't done the
analysis since.  Anyways, it should be documented.

> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> ---
> ---
>  arch/x86/kvm/cpuid.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index d2f93823f9fd..5decc2dd5448 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -121,6 +121,8 @@ void kvm_update_vcpu_model(struct kvm_vcpu *vcpu)
>  	struct kvm_lapic *apic = vcpu->arch.apic;
>  	struct kvm_cpuid_entry2 *best;
>  
> +	kvm_x86_ops.update_vcpu_model(vcpu);
> +
>  	best = kvm_find_cpuid_entry(vcpu, 1, 0);
>  	if (best && apic) {
>  		if (cpuid_entry_has(best, X86_FEATURE_TSC_DEADLINE_TIMER))
> @@ -136,6 +138,7 @@ void kvm_update_vcpu_model(struct kvm_vcpu *vcpu)
>  		vcpu->arch.guest_supported_xcr0 =
>  			(best->eax | ((u64)best->edx << 32)) & supported_xcr0;
>  
> +

Spurious whitespace.

>  	/* Note, maxphyaddr must be updated before tdp_level. */
>  	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
>  	vcpu->arch.tdp_level = kvm_x86_ops.get_tdp_level(vcpu);
> @@ -224,7 +227,6 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
>  
>  	cpuid_fix_nx_cap(vcpu);
>  	kvm_apic_set_version(vcpu);
> -	kvm_x86_ops.update_vcpu_model(vcpu);
>  	kvm_update_cpuid(vcpu);
>  	kvm_update_vcpu_model(vcpu);
>  
> @@ -254,7 +256,6 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
>  	}
>  
>  	kvm_apic_set_version(vcpu);
> -	kvm_x86_ops.update_vcpu_model(vcpu);
>  	kvm_update_cpuid(vcpu);
>  	kvm_update_vcpu_model(vcpu);
>  out:
> -- 
> 2.18.2
>