iommu/amd: Block identity domain when SNP enabled

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 <[e-mail]>
Reviewed-by: Vasant Hegde <[e-mail]>
Reviewed-by: Jason Gunthorpe <[e-mail]>
Signed-off-by: Joerg Roedel <[e-mail]>

drivers/iommu/amd/iommu.c

···
 
 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)