Re: [PATCH] iommu/amd: Block identity domain when SNP enabled

[Vasant Hegde <vasant.hegde@amd.com>]

On 3/10/2026 5:22 AM, Joe Damato wrote:
> 
> Previously, commit 8388f7df936b ("iommu/amd: Do not support
> IOMMU_DOMAIN_IDENTITY after SNP is enabled") prevented users from
> changing the IOMMU domain to identity if SNP was enabled.
> 
> This resulted in an error when writing to sysfs:
> 
>   # echo "identity" > /sys/kernel/iommu_groups/50/type
>   -bash: echo: write error: Cannot allocate memory
> 
> However, commit 4402f2627d30 ("iommu/amd: Implement global identity
> domain") changed the flow of the code, skipping the SNP guard and
> allowing users to change the IOMMU domain to identity after a machine
> has booted.
> 
> Once the user does that, they will probably try to bind and the
> device/driver will start to do DMA which will trigger errors:
> 
>   iommu ivhd3: AMD-Vi: Event logged [ILLEGAL_DEV_TABLE_ENTRY device=0000:43:00.0 pasid=0x00000 address=0x3737b01000 flags=0x0020]
>   iommu ivhd3: AMD-Vi: Control Reg : 0xc22000142148d
>   AMD-Vi: DTE[0]: 6000000000000003
>   AMD-Vi: DTE[1]: 0000000000000001
>   AMD-Vi: DTE[2]: 2000003088b3e013
>   AMD-Vi: DTE[3]: 0000000000000000
>   bnxt_en 0000:43:00.0 (unnamed net_device) (uninitialized): Error (timeout: 500015) msg {0x0 0x0} len:0
>   iommu ivhd3: AMD-Vi: Event logged [ILLEGAL_DEV_TABLE_ENTRY device=0000:43:00.0 pasid=0x00000 address=0x3737b01000 flags=0x0020]
>   iommu ivhd3: AMD-Vi: Control Reg : 0xc22000142148d
>   AMD-Vi: DTE[0]: 6000000000000003
>   AMD-Vi: DTE[1]: 0000000000000001
>   AMD-Vi: DTE[2]: 2000003088b3e013
>   AMD-Vi: DTE[3]: 0000000000000000
>   bnxt_en 0000:43:00.0: probe with driver bnxt_en failed with error -16
> 
> To prevent this from happening, create an attach wrapper for
> identity_domain_ops which returns EINVAL if amd_iommu_snp_en is true.
> 
> With this commit applied:
> 
>   # echo "identity" > /sys/kernel/iommu_groups/62/type
>   -bash: echo: write error: Invalid argument
> 
> Fixes: 4402f2627d30 ("iommu/amd: Implement global identity domain")
> Signed-off-by: Joe Damato <joe@dama.to>

Thanks for the fix.

Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>

-Vasant