linux-kernel - Re: [PATCH] KVM: x86: use correct APIC ID on x2APIC transition

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Date:	Tue, 26 May 2015 12:38:17 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>,
	linux-kernel@...r.kernel.org
CC:	kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: use correct APIC ID on x2APIC transition



On 22/05/2015 18:45, Radim Krčmář wrote:
> SDM April 2015, 10.12.5 State Changes From xAPIC Mode to x2APIC Mode
> • Any APIC ID value written to the memory-mapped local APIC ID register
>   is not preserved.
> 
> Fix it by sourcing vcpu_id (= initial APIC ID) instead of memory-mapped
> APIC ID.  Proper use of apic functions would result in two calls to
> recalculate_apic_map(), so this patch makes a new helper.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  arch/x86/kvm/lapic.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index dc5b57bb1f76..c2a7d8a7a414 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -240,6 +240,15 @@ static inline void kvm_apic_set_ldr(struct kvm_lapic *apic, u32 id)
>  	recalculate_apic_map(apic->vcpu->kvm);
>  }
>  
> +static inline void kvm_apic_set_x2apic_id(struct kvm_lapic *apic, u8 id)
> +{
> +	u32 ldr = ((id >> 4) << 16) | (1 << (id & 0xf));
> +
> +	apic_set_reg(apic, APIC_ID, id << 24);
> +	apic_set_reg(apic, APIC_LDR, ldr);
> +	recalculate_apic_map(apic->vcpu->kvm);
> +}
> +
>  static inline int apic_lvt_enabled(struct kvm_lapic *apic, int lvt_type)
>  {
>  	return !(kvm_apic_get_reg(apic, lvt_type) & APIC_LVT_MASKED);
> @@ -1538,9 +1547,7 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
>  
>  	if ((old_value ^ value) & X2APIC_ENABLE) {
>  		if (value & X2APIC_ENABLE) {
> -			u32 id = kvm_apic_id(apic);
> -			u32 ldr = ((id >> 4) << 16) | (1 << (id & 0xf));
> -			kvm_apic_set_ldr(apic, ldr);
> +			kvm_apic_set_x2apic_id(apic, vcpu->vcpu_id);
>  			kvm_x86_ops->set_virtual_x2apic_mode(vcpu, true);
>  		} else
>  			kvm_x86_ops->set_virtual_x2apic_mode(vcpu, false);
> 

Applied, thanks.

Paolo
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