Re: [Xen-devel] [PATCH v12 7/7] passthrough/io: Fall back to remapping interrupt when we can't use VT-d PI

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.04.17 at 02:30, <chao.gao@xxxxxxxxx> wrote:
> The current logic of using VT-d pi is when guest configurates the pirq's
> destination vcpu to a single vcpu, the according IRTE is updated to
> posted format. If the destination of the pirq is multiple vcpus, we will
> stay in posted format. Obviously, we should fall back to remapping interrupt
> when guest wrongly configurate destination of pirq or makes it have
> multi-destination vcpus.
> 
> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> ---
> v11:
> - move the code (one line) that allow the parameter 'vcpu' of pi_update_irte()
> can be NULL to Patch [2/6].

There was a change in v12 too, and I'm afraid it's buggy:

> --- a/xen/drivers/passthrough/io.c
> +++ b/xen/drivers/passthrough/io.c
> @@ -413,15 +413,8 @@ int pt_irq_create_bind(
>  
>          /* Use interrupt posting if it is supported. */
>          if ( iommu_intpost )
> -        {
> -            if ( vcpu )
> -                pi_update_irte(&vcpu->arch.hvm_vmx.pi_desc, info,
> -                               pirq_dpci->gmsi.gvec);
> -            else
> -                dprintk(XENLOG_G_INFO,
> -                        "%pv: deliver interrupt in remapping 
> mode,gvec:%02x\n",
> -                        vcpu, pirq_dpci->gmsi.gvec);
> -        }
> +            pi_update_irte(&vcpu->arch.hvm_vmx.pi_desc, info,
> +                           pirq_dpci->gmsi.gvec);

pi_update_irte() tolerates a NULL first argument, but if vcpu is NULL
you don't pass NULL here. I'll fix this up while committing.

Jan


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