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

From: "Deucher, Alexander" <Alexander.Deucher@amd.com>
To: Joerg Roedel <joro@8bytes.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	"Kuehling, Felix" <Felix.Kuehling@amd.com>,
	"Koenig, Christian" <Christian.Koenig@amd.com>
Cc: "Lendacky, Thomas" <Thomas.Lendacky@amd.com>,
	"jroedel@suse.de" <jroedel@suse.de>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 1/2] iommu/amd: Do not force direct mapping when SME is active
Date: Wed, 26 Aug 2020 14:23:44 +0000	[thread overview]
Message-ID: <MN2PR12MB44887D5839767CFF49C24696F7540@MN2PR12MB4488.namprd12.prod.outlook.com> (raw)
In-Reply-To: <20200824105415.21000-2-joro@8bytes.org>

[AMD Public Use]

+ Felix, Christian

> -----Original Message-----
> From: Joerg Roedel <joro@8bytes.org>
> Sent: Monday, August 24, 2020 6:54 AM
> To: iommu@lists.linux-foundation.org
> Cc: Joerg Roedel <joro@8bytes.org>; jroedel@suse.de; Lendacky, Thomas
> <Thomas.Lendacky@amd.com>; Suthikulpanit, Suravee
> <Suravee.Suthikulpanit@amd.com>; Deucher, Alexander
> <Alexander.Deucher@amd.com>; linux-kernel@vger.kernel.org
> Subject: [PATCH 1/2] iommu/amd: Do not force direct mapping when SME is
> active
> 
> From: Joerg Roedel <jroedel@suse.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@suse.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
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