Re: [Xen-devel] [v4 09/17] vmx: Suppress posting interrupts when 'SN' is set

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.07.15 at 13:35, <feng.wu@xxxxxxxxx> wrote:
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -1697,14 +1697,39 @@ static void vmx_deliver_posted_intr(struct vcpu *v, 
> u8 vector)
>           * VMEntry as it used to be.
>           */
>          pi_set_on(&v->arch.hvm_vmx.pi_desc);
> +        vcpu_kick(v);

Why can't this be left at the end of the function? You only need to ...

>      }
> -    else if ( !pi_test_and_set_on(&v->arch.hvm_vmx.pi_desc) )
> +    else
>      {
> +        struct pi_desc old, new, prev;
> +
> +        prev.control = 0;
> +
> +        do {
> +            /*
> +             * Currently, we don't support urgent interrupt, all
> +             * interrupts are recognized as non-urgent interrupt,
> +             * so we cannot send posted-interrupt when 'SN' is set.
> +             * Besides that, if 'ON' is already set, we cannot set
> +             * posted-interrupts as well.
> +             */
> +            if ( pi_test_sn(&prev) || pi_test_on(&prev) )
> +            {
> +                vcpu_kick(v);
> +                return;
> +            }
> +
> +            old.control = v->arch.hvm_vmx.pi_desc.control &
> +                          ~( 1 << POSTED_INTR_ON | 1 << POSTED_INTR_SN );
> +            new.control = v->arch.hvm_vmx.pi_desc.control |
> +                          1 << POSTED_INTR_ON;
> +
> +            prev.control = cmpxchg(&v->arch.hvm_vmx.pi_desc.control,
> +                                   old.control, new.control);
> +        } while ( prev.control != old.control );
> +
>          __vmx_deliver_posted_interrupt(v);
> -        return;

... keep the return here.

>      }
> -
> -    vcpu_kick(v);
>  }

Makes for a smaller and hence more obviously correct change. Or am
I overlooking something?

Jan


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