[PATCH v1] iommu: Skip mapping at address 0x0 if it already exists

[Antheas Kapenekakis <lkml@antheas.dev>]

Commit 789a5913b29c ("iommu/amd: Use the generic iommu page table")
introduces the shared iommu page table for AMD IOMMU. Some bioses
contain an identity mapping for address 0x0, which is not parsed
properly (e.g., certain Strix Halo devices). This causes the DMA
components of the device to fail to initialize (e.g., the NVMe SSD
controller), leading to a failed post.

The failure is caused by iommu_create_device_direct_mappings(), which
is the new mapping implementation. In it, address aliasing is handled
via the following check:

```
phys_addr = iommu_iova_to_phys(domain, addr);
if (!phys_addr) {
        map_size += pg_size;
        continue;
}
````

Obviously, the iommu_iova_to_phys() signature is faulty and aliases
unmapped and 0 together, causing the allocation code to try to
re-allocate the 0 address per device. However, it has too many
instantiations to fix. Therefore, catch ret == -EADDRINUSE only when
addr == 0 and, instead of bailing, skip the mapping and print a warning.

Closes: https://www.reddit.com/r/cachyos/comments/1r5sgr6/freeze_on_boot_after_kernel_update_to_619_fixed/
Fixes: 789a5913b29c ("iommu/amd: Use the generic iommu page table")
Signed-off-by: Antheas Kapenekakis <lkml@antheas.dev>
---
 drivers/iommu/iommu.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 4926a43118e6..d424b7124311 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1224,6 +1224,11 @@ static int iommu_create_device_direct_mappings(struct iommu_domain *domain,
 				ret = iommu_map(domain, addr - map_size,
 						addr - map_size, map_size,
 						entry->prot, GFP_KERNEL);
+				if (ret == -EADDRINUSE && addr - map_size == 0) {
+					dev_warn_once(dev,
+						"iommu: identity mapping at addr 0x0 already exists, skipping\n");
+					ret = 0;
+				}
 				if (ret)
 					goto out;
 				map_size = 0;

base-commit: 57d76ceccee4b497eb835831206b50e72915a501
-- 
2.52.0