linux-kernel - RE: [PATCH 1/2] iommu/amd: Do not force direct mapping when SME is active

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Date:   Wed, 26 Aug 2020 14:23:44 +0000
From:   "Deucher, Alexander" <Alexander.Deucher@....com>
To:     Joerg Roedel <joro@...tes.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "Kuehling, Felix" <Felix.Kuehling@....com>,
        "Koenig, Christian" <Christian.Koenig@....com>
CC:     "jroedel@...e.de" <jroedel@...e.de>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] iommu/amd: Do not force direct mapping when SME is
 active

[AMD Public Use]

+ Felix, Christian

> -----Original Message-----
> From: Joerg Roedel <joro@...tes.org>
> Sent: Monday, August 24, 2020 6:54 AM
> To: iommu@...ts.linux-foundation.org
> Cc: Joerg Roedel <joro@...tes.org>; jroedel@...e.de; Lendacky, Thomas
> <Thomas.Lendacky@....com>; Suthikulpanit, Suravee
> <Suravee.Suthikulpanit@....com>; Deucher, Alexander
> <Alexander.Deucher@....com>; linux-kernel@...r.kernel.org
> Subject: [PATCH 1/2] iommu/amd: Do not force direct mapping when SME is
> active
> 
> From: Joerg Roedel <jroedel@...e.de>
> 
> Do not force devices supporting IOMMUv2 to be direct mapped when
> memory encryption is active. This might cause them to be unusable because
> their DMA mask does not include the encryption bit.
> 
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
>  drivers/iommu/amd/iommu.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index ba9f3dbc5b94..77e4268e41cf 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -2659,7 +2659,12 @@ static int amd_iommu_def_domain_type(struct
> device *dev)
>  	if (!dev_data)
>  		return 0;
> 
> -	if (dev_data->iommu_v2)
> +	/*
> +	 * Do not identity map IOMMUv2 capable devices when memory
> encryption is
> +	 * active, because some of those devices (AMD GPUs) don't have the
> +	 * encryption bit in their DMA-mask and require remapping.
> +	 */

I think on the integrated GPUs in APUs I'd prefer to have the identity mapping over SME, but I guess this is fine because you have to explicitly enable SME and if you do that you know what you are getting into.

Alex

> +	if (!mem_encrypt_active() && dev_data->iommu_v2)
>  		return IOMMU_DOMAIN_IDENTITY;
> 
>  	return 0;
> --
> 2.28.0