[PATCH 6/7] vfio/cdx: keep logical vm_pgoff in MMIO region mmap

[Abdifatah Suruur]

vfio_cdx_mmap_mmio() overwrites vma->vm_pgoff with the physical frame
number of the MMIO region and passes it to io_remap_pfn_range().  The
VMA is inserted into the device file's mapping->i_mmap interval tree
keyed by vm_pgoff, which VFIO expects to be the logical file offset:
the core links every device mmap to the device inode's i_mapping
precisely so that unmap_mapping_range() can revoke all mappings
associated with a device (see vfio_device_cdev_open()).

With a raw PFN in vm_pgoff the interval tree entry lands in the wrong
coordinate space and unmap_mapping_range() cannot find the VMA,
leaving stale MMIO mappings behind any revocation attempt.  Keep
vm_pgoff in the logical VFIO offset space, as vfio-pci does, and pass
the physical PFN to io_remap_pfn_range() explicitly.

This is defensive hygiene: none of vfio-platform, vfio/fsl-mc and
vfio/cdx call unmap_mapping_range() today, so no reachable
stale-mapping issue exists.  Keeping vm_pgoff logical preserves the
VFIO core contract for any future revocation path.

Signed-off-by: Abdifatah Suruur <suruurism@xxxxxxxxx>
---
--- a/drivers/vfio/cdx/main.c
+++ b/drivers/vfio/cdx/main.c
@@ -257,6 +257,6 @@
-	vma->vm_pgoff = (region.addr >> PAGE_SHIFT) + pgoff;
 	vma->vm_page_prot = pgprot_device(vma->vm_page_prot);

-	return io_remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
+	return io_remap_pfn_range(vma, vma->vm_start,
+				  (region.addr >> PAGE_SHIFT) + pgoff,
 				  size, vma->vm_page_prot);
 }