Re: [Xen-devel] [PATCH v2] x86/vlapic: Don't reset APIC ID when handling INIT signal

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.04.17 at 08:40, <chao.gao@xxxxxxxxx> wrote:
> @@ -1257,7 +1257,12 @@ void vlapic_reset(struct vlapic *vlapic)
>      }
>      vlapic_set_reg(vlapic, APIC_ICR,     0);
>      vlapic_set_reg(vlapic, APIC_ICR2,    0);
> -    vlapic_set_reg(vlapic, APIC_LDR,     0);
> +    /*
> +     * LDR is read-only in x2APIC mode. Preserve its value when handling
> +     * INIT signal in x2APIC mode.
> +     */
> +    if ( !vlapic_x2apic_mode(vlapic) )

In order for this to work you need to ...

> +        vlapic_set_reg(vlapic, APIC_LDR, 0);
>      vlapic_set_reg(vlapic, APIC_TASKPRI, 0);
>      vlapic_set_reg(vlapic, APIC_TMICT,   0);
>      vlapic_set_reg(vlapic, APIC_TMCCT,   0);
> @@ -1275,6 +1280,22 @@ void vlapic_reset(struct vlapic *vlapic)
>      destroy_periodic_time(&vlapic->pt);
>  }
>  
> +/* Reset the VLAPIC back to its power-on/reset state. */
> +void vlapic_reset(struct vlapic *vlapic)
> +{
> +    const struct vcpu *v = vlapic_vcpu(vlapic);
> +
> +    if ( !has_vlapic(v->domain) )
> +        return;
> +
> +    vlapic_set_reg(vlapic, APIC_ID, (v->vcpu_id * 2) << 24);
> +    vlapic_set_reg(vlapic, APIC_LDR, 0);
> +    vlapic_do_init(vlapic);
> +
> +    vlapic->hw.apic_base_msr &= ~(uint64_t)MSR_IA32_APICBASE_EXTD;

... do this before calling vlapic_do_init() afaict (and I see no strong
reason why you would need a cast here)). Likely it is a good idea
then to also ...

> +    vlapic->hw.apic_base_msr |= MSR_IA32_APICBASE_ENABLE;

... do this up front.

> @@ -1489,8 +1510,7 @@ int vlapic_init(struct vcpu *v)
>  
>      vlapic_reset(vlapic);
>  
> -    vlapic->hw.apic_base_msr = (MSR_IA32_APICBASE_ENABLE |
> -                                APIC_DEFAULT_PHYS_BASE);
> +    vlapic->hw.apic_base_msr |= APIC_DEFAULT_PHYS_BASE;

Perhaps better move this ahead of the call to vlapic_reset() then
too.

Remains the question (not answered by the SDM afaics): What
happens to the base address during reset?

Jan


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