iommu/amd: Force identity mode for selected GPUs only

Certain AMD GPUs must always operate in IOMMU identity mode. This was
previously enforced using a PASID check, which happened to work because
these specific GPUs are PASID-capable. However, this approach incorrectly
applies identity mode enforcement to all PASID-capable devices, not just
the GPUs that require it.

This made sense in the past because the domain allocation API
(iommu_ops->domain_alloc()) only received the domain type, so the
driver had no way to inspect device capabilities and pick the most
suitable page table format (v1 or v2). With the recent driver
enhancement to use domain_alloc_paging_flags() for all paging
domain allocations, the driver can now inspect the device and flags
directly and choose the appropriate page table type per device.

Update amd_iommu_def_domain_type() to force identity mapping only for
the specific GPUs that require it, via a new quirks_force_identity_mapping().

With this change, a system booting in DMA translation mode will now
select:
 * Guest (v2) page table for PASID-capable devices
 * Host (v1) page table for non-PASID-capable devices

Also drop the amd_iommu_snp_en check, as SNP enforces paging domain,
which doesn't work with the identity requirement of these GPUs.

Link: https://lore.kernel.org/all/20200824105415.21000-1-joro@8bytes.org/
Link: https://lore.kernel.org/linux-iommu/20260723061548.10187-1-vasant.hegde@amd.com/
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

0 files changed, 0 insertions, 0 deletions