[PATCH v2] fuse: mark DAX VMA page protections as decrypted

[Punit Salian <psalian@google.com>]

In confidential computing guest environments (such as AMD SEV-SNP or
Intel TDX), direct memory access (DAX) mappings between the guest kernel
and host-backed FUSE/virtiofs shared memory regions must be accessed
using shared (decrypted) page protections.

Modify fuse_dax_mmap() to apply pgprot_decrypted() to vma->vm_page_prot
when establishing FUSE DAX memory mappings. This ensures guest page
table entries for shared DAX buffers are explicitly marked as decrypted,
preventing memory encryption faults when accessing host-shared DAX memory.

Signed-off-by: Punit Salian <psalian@google.com>
Acked-by: Pankaj Gupta <pankaj.gupta@amd.com>
---
v1 -> v2:
- Added Acked-by tag from Pankaj Gupta.
---
 fs/fuse/dax.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
index a15c464c8d19..00e316a7f805 100644
--- a/fs/fuse/dax.c
+++ b/fs/fuse/dax.c
@@ -826,6 +826,7 @@ int fuse_dax_mmap(struct file *file, struct vm_area_struct *vma)
 	file_accessed(file);
 	vma->vm_ops = &fuse_dax_vm_ops;
 	vm_flags_set(vma, VM_MIXEDMAP | VM_HUGEPAGE);
+	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
 
 	return 0;
 }
--