Re: [Xen-devel] [PATCH] x86/hvm/viridian: save APIC assist vector

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.03.16 at 18:19, <paul.durrant@xxxxxxxxxx> wrote:
> @@ -293,10 +292,11 @@ void viridian_start_apic_assist(struct vcpu *v, int 
> vector)
>       * wrong and the VM will most likely hang so force a crash now
>       * to make the problem clear.
>       */
> -    if ( v->arch.hvm_vcpu.viridian.apic_assist.vector >= 0 )
> +    if ( v->arch.hvm_vcpu.viridian.apic_assist.vector != 0 )
>          domain_crash(v->domain);
>  
> -    v->arch.hvm_vcpu.viridian.apic_assist.vector = vector;
> +    /* Increment the value so that zero is always invalid. */
> +    v->arch.hvm_vcpu.viridian.apic_assist.vector = vector + 1;

From an APIC perspective, aren't vectors below 0x10 invalid
anyway? I.e. can't zero serve the "none" indication just as much
as -1 did without this new biasing? Or otherwise I'd still expect ...

> @@ -829,13 +830,21 @@ static int viridian_load_vcpu_ctxt(struct domain *d, 
> hvm_domain_context_t *h)
>          return -EINVAL;
>      }
>  
> -    if ( hvm_load_entry(VIRIDIAN_VCPU, h, &ctxt) != 0 )
> +    if ( hvm_load_entry_zeroextend(VIRIDIAN_VCPU, h, &ctxt) != 0 )
>          return -EINVAL;
>  
> -    v->arch.hvm_vcpu.viridian.apic_assist.msr.raw = ctxt.apic_assist;
> +    v->arch.hvm_vcpu.viridian.apic_assist.msr.raw = ctxt.apic_assist_msr;
>      if ( v->arch.hvm_vcpu.viridian.apic_assist.msr.fields.enabled )
>          initialize_apic_assist(v);
>  
> +    /*
> +     * Guests that were saved on a host that did not use APIC assist
> +     * will clearly never have a pending assist, so reading the zero
> +     * value for apic_assist_vector from the zero extended save record
> +     * will always be correct.
> +     */
> +    v->arch.hvm_vcpu.viridian.apic_assist.vector = ctxt.apic_assist_vector;

... the bias to get accounted for here, instead of quite a bit of
other code getting adjusted, and the meaning of the "vector"
field getting slightly mis-used.

Jan


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