[PATCH] iommu/amd: Do not identity map v2 capable device when snp is enabled

[PATCH] iommu/amd: Do not identity map v2 capable device when snp is enabled

[Vasant Hegde]

Flow:
  - Booted system with SNP enabled, memory encryption off and
    IOMMU DMA translation mode
  - AMD driver detects v2 capable device and amd_iommu_def_domain_type()
    returns identity mode
  - amd_iommu_domain_alloc() returns NULL an SNP is enabled
  - System will fail to register device

On SNP enabled system, passthrough mode is not supported. IOMMU default
domain is set to translation mode. We need to return zero from
amd_iommu_def_domain_type() so that it allocates translation domain.

Fixes: fb2accadaa942 (iommu/amd: Introduce function to check and enable SNP)
CC: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
---
 drivers/iommu/amd/iommu.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 0b011a97e20d..3186e0dd8b2b 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -2401,12 +2401,17 @@ static int amd_iommu_def_domain_type(struct device *dev)
 		return 0;
 
 	/*
-	 * 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.
+	 * 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.
+	 *  - SNP is enabled, because it prohibits DTE[Mode]=0.
 	 */
-	if (!cc_platform_has(CC_ATTR_MEM_ENCRYPT) && dev_data->iommu_v2)
+	if (dev_data->iommu_v2 &&
+	    !cc_platform_has(CC_ATTR_MEM_ENCRYPT) &&
+	    !amd_iommu_snp_en) {
 		return IOMMU_DOMAIN_IDENTITY;
+	}
 
 	return 0;
 }
-- 
2.31.1

Re: [PATCH] iommu/amd: Do not identity map v2 capable device when snp is enabled

[Joerg Roedel]

Hi Vasant,

On Tue, Feb 07, 2023 at 09:17:52AM +0000, Vasant Hegde wrote:
>  drivers/iommu/amd/iommu.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)

Applied and fixed a checkpatch warning. Please use check-patch in the
future before submitting.

Regards,

	Joerg

Re: [PATCH] iommu/amd: Do not identity map v2 capable device when snp is enabled

[Vasant Hegde]

Joerg,

On 2/16/2023 3:17 PM, Joerg Roedel wrote:
> Hi Vasant,
> 
> On Tue, Feb 07, 2023 at 09:17:52AM +0000, Vasant Hegde wrote:
>>  drivers/iommu/amd/iommu.c | 13 +++++++++----
>>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> Applied and fixed a checkpatch warning. Please use check-patch in the
> future before submitting.

Sure. Thank you.

-Vasant