linux-kernel - Re: [RFC PATCH 6/7] iommu/amd: Introduce amd_iommu

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Date:   Thu, 18 Mar 2021 16:33:36 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Jon.Grimm@....com, Wei.Huang2@....com
Subject: Re: [RFC PATCH 6/7] iommu/amd: Introduce amd_iommu_pgtable
 command-line option

On Fri, Mar 12, 2021 at 03:04:10AM -0600, Suravee Suthikulpanit wrote:
> To allow specification whether to use v1 or v2 IOMMU pagetable for
> DMA remapping when calling kernel DMA-API.
> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  6 ++++++
>  drivers/iommu/amd/init.c                        | 15 +++++++++++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 04545725f187..466e807369ea 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -319,6 +319,12 @@
>  			             This mode requires kvm-amd.avic=1.
>  			             (Default when IOMMU HW support is present.)
>  
> +	amd_iommu_pgtable= [HW,X86-64]
> +			Specifies one of the following AMD IOMMU page table to
> +			be used for DMA remapping for DMA-API:
> +			v1         - Use v1 page table (Default)
> +			v2         - Use v2 page table

Any reason v2 can not be the default when it is supported by the IOMMU?