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Re: [Xen-devel] [PATCH] AMD/IOMMU: correct handling when XT's prereq features are unavailable


  • To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Thu, 27 Feb 2020 15:25:08 +0000
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  • Delivery-date: Thu, 27 Feb 2020 15:25:21 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 27/02/2020 14:34, Jan Beulich wrote:
> --- a/xen/drivers/passthrough/amd/iommu_init.c
> +++ b/xen/drivers/passthrough/amd/iommu_init.c
> @@ -1364,6 +1364,7 @@ static int __init amd_iommu_prepare_one(
>  int __init amd_iommu_prepare(bool xt)
>  {
>      struct amd_iommu *iommu;
> +    bool no_xt = false;

I think the logic would be easier to follow if this was has_xt, with
inverted meaning.  However...

>      int rc = -ENODEV;
>  
>      BUG_ON( !iommu_found() );
> @@ -1400,9 +1401,8 @@ int __init amd_iommu_prepare(bool xt)
>          if ( rc )
>              goto error_out;
>  
> -        rc = -ENODEV;
> -        if ( xt && (!iommu->features.flds.ga_sup || 
> !iommu->features.flds.xt_sup) )
> -            goto error_out;
> +        if ( !iommu->features.flds.ga_sup || !iommu->features.flds.xt_sup )
> +            no_xt = true;
>      }
>  
>      for_each_amd_iommu ( iommu )

... the contents of this loop depends on the early exit path you've just
deleted.

In the case of x2apic not being available, we'll still set {ga,xt}_en to
the caller requested value.

~Andrew

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