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>
---
 drivers/iommu/amd/iommu.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 81c4d7733872..760d5f4623b5 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -2909,8 +2909,21 @@ static struct iommu_domain blocked_domain = {
 
 static struct protection_domain identity_domain;
 
+static int amd_iommu_identity_attach(struct iommu_domain *dom, struct device *dev,
+				     struct iommu_domain *old)
+{
+	/*
+	 * Don't allow attaching a device to the identity domain if SNP is
+	 * enabled.
+	 */
+	if (amd_iommu_snp_en)
+		return -EINVAL;
+
+	return amd_iommu_attach_device(dom, dev, old);
+}
+
 static const struct iommu_domain_ops identity_domain_ops = {
-	.attach_dev = amd_iommu_attach_device,
+	.attach_dev = amd_iommu_identity_attach,
 };
 
 void amd_iommu_init_identity_domain(void)
-- 
2.52.0

On Mon, Mar 09, 2026 at 04:52:33PM -0700, Joe Damato wrote:
>  drivers/iommu/amd/iommu.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)

Applied, thanks.

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

On Mon, Mar 09, 2026 at 04:52:33PM -0700, Joe Damato wrote:
> 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>
> ---
>  drivers/iommu/amd/iommu.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason