[PATCH] resource: export iomem_get_mapping() for loadable modules

[Ravi Kumar Bandi <ravib@amazon.com>]

Loadable PCIe driver modules that handle surprise removal or link-down
events need to zap userspace mappings of PCI BAR resources to deliver
SIGBUS on next access, rather than leaving stale mappings to a dead
device.

The correct way to do this is via unmap_mapping_range() on the iomem
address space, which is already exported via EXPORT_SYMBOL.
However, iomem_get_mapping() which returns the iomem address space
is not exported, making it impossible to use unmap_mapping_range()
correctly from a loadable module without resorting to workarounds
such as walking all process VMAs or opening /dev/mem.

Export iomem_get_mapping() via EXPORT_SYMBOL_GPL to complete the
existing exported API and allow loadable modules to properly zap
PCI BAR mappings on device removal.

Signed-off-by: Ravi Kumar Bandi <ravib@amazon.com>
---
 kernel/resource.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/resource.c b/kernel/resource.c
index d02a53fb95d8..8801e390fe2e 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1311,6 +1311,7 @@ struct address_space *iomem_get_mapping(void)
 	 */
 	return smp_load_acquire(&iomem_inode)->i_mapping;
 }
+EXPORT_SYMBOL_GPL(iomem_get_mapping);
 
 static int __request_region_locked(struct resource *res, struct resource *parent,
 				   resource_size_t start, resource_size_t n,
-- 
2.47.3