Re: [PATCH 5/5] KVM: x86: BSP in MSR_IA32_APICBASE is writable

[Paolo Bonzini <pbonzini@redhat.com>]

On 30/03/2015 14:39, Nadav Amit wrote:
> After reset, the CPU can change the BSP, which will be used upon INIT.  Reset
> should return the BSP which QEMU asked for, and therefore handled accordingly.
> 
> To quote: "If the MP protocol has completed and a BSP is chosen, subsequent
> INITs (either to a specific processor or system wide) do not cause the MP
> protocol to be repeated."
> [Intel SDM 8.4.2: MP Initialization Protocol Requirements and Restrictions]
> 
> Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>

Please provide a kvm-unit-tests testcase for this.

Paolo

> ---
>  arch/x86/kvm/lapic.c     | 2 --
>  arch/x86/kvm/svm.c       | 2 +-
>  arch/x86/kvm/vmx.c       | 2 +-
>  include/linux/kvm_host.h | 7 ++++++-
>  4 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 17da6fc..b0dbf68 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1498,8 +1498,6 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
>  		return;
>  	}
>  
> -	if (!kvm_vcpu_is_bsp(apic->vcpu))
> -		value &= ~MSR_IA32_APICBASE_BSP;
>  	vcpu->arch.apic_base = value;
>  
>  	/* update jump label if enable bit changes */
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 1ef4c0d..ef5bf21 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1261,7 +1261,7 @@ static struct kvm_vcpu *svm_create_vcpu(struct kvm *kvm, unsigned int id)
>  
>  	svm->vcpu.arch.apic_base = APIC_DEFAULT_PHYS_BASE |
>  				   MSR_IA32_APICBASE_ENABLE;
> -	if (kvm_vcpu_is_bsp(&svm->vcpu))
> +	if (kvm_vcpu_is_reset_bsp(&svm->vcpu))
>  		svm->vcpu.arch.apic_base |= MSR_IA32_APICBASE_BSP;
>  
>  	svm_init_osvw(&svm->vcpu);
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 8aee6db..7e370b2 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -4709,7 +4709,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>  	if (!init_event) {
>  		apic_base_msr.data = APIC_DEFAULT_PHYS_BASE |
>  				     MSR_IA32_APICBASE_ENABLE;
> -		if (kvm_vcpu_is_bsp(&vmx->vcpu))
> +		if (kvm_vcpu_is_reset_bsp(&vmx->vcpu))
>  			apic_base_msr.data |= MSR_IA32_APICBASE_BSP;
>  		apic_base_msr.host_initiated = true;
>  		kvm_set_apic_base(&vmx->vcpu, &apic_base_msr);
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 0f574eb..8365cae 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -968,11 +968,16 @@ static inline int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
>  #endif /* CONFIG_HAVE_KVM_EVENTFD */
>  
>  #ifdef CONFIG_KVM_APIC_ARCHITECTURE
> -static inline bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu)
> +static inline bool kvm_vcpu_is_reset_bsp(struct kvm_vcpu *vcpu)
>  {
>  	return vcpu->kvm->bsp_vcpu_id == vcpu->vcpu_id;
>  }
>  
> +static inline bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu)
> +{
> +	return (vcpu->arch.apic_base & MSR_IA32_APICBASE_BSP) != 0;
> +}
> +
>  bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu);
>  
>  #else
>