[PATCH 4/7] vfio/platform: keep logical vm_pgoff in MMIO region mmap

[Abdifatah Suruur <suruurism@gmail.com>]

vfio_platform_mmap_mmio() overwrites vma->vm_pgoff with the physical
frame number of the MMIO region and passes it to 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 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@gmail.com>
---
--- a/drivers/vfio/platform/vfio_platform_common.c
+++ b/drivers/vfio/platform/vfio_platform_common.c
@@ -561,6 +561,5 @@
 	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
-	vma->vm_pgoff = (region.addr >> PAGE_SHIFT) + pgoff;
-
-	return remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
+	return remap_pfn_range(vma, vma->vm_start,
+			       (region.addr >> PAGE_SHIFT) + pgoff,
 			       req_len, vma->vm_page_prot);
 }