iommu/vt-d: Make iotlb_sync_map a static property of dmar_domain

iommu/vt-d: Make iotlb_sync_map a static property of dmar_domain

Commit 12724ce3fe1a ("iommu/vt-d: Optimize iotlb_sync_map for
non-caching/non-RWBF modes") dynamically set iotlb_sync_map. This causes
synchronization issues due to lack of locking on map and attach paths,
racing iommufd userspace operations.

Invalidation changes must precede device attachment to ensure all flushes
complete before hardware walks page tables, preventing coherence issues.

Make domain->iotlb_sync_map static, set once during domain allocation. If
an IOMMU requires iotlb_sync_map but the domain lacks it, attach is
rejected. This won't reduce domain sharing: RWBF and shadowing page table
caching are legacy uses with legacy hardware. Mixed configs (some IOMMUs
in caching mode, others not) are unlikely in real-world scenarios.

Fixes: 12724ce3fe1a ("iommu/vt-d: Optimize iotlb_sync_map for non-caching/non-RWBF modes")
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20250721051657.1695788-1-baolu.lu@linux.intel.com
Signed-off-by: Will Deacon <will@kernel.org>