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

[Christoph Hellwig]

On Mon, May 11, 2026 at 04:16:43PM +0000, Ravi Kumar Bandi wrote:
> On Mon, May 11, 2026 at 00:17:45 -0700, Christoph Hellwig wrote:
> > And why?
> 
> On Mon, May 11, 2026 at 09:14:04 +0200, David Hildenbrand wrote:
> > Which in-tree driver wants to make use of this?
> 
> Thank you both for reviewing the patch.
> 
> Currently this is needed by a PCIe endpoint driver that handles surprise
> removal on a device without a hot-plug pin routed to the CPU.

Which endpoint driver?

> When link-down is detected, the endpoint driver needs to zap existing
> userspace BAR mappings (mmap'd via sysfs resource files) to deliver SIGBUS
> rather than leaving stale mappings to a dead device, preventing kernel
> crashes on subsequent accesses.

Why would the endpoint driver map iomem to userspace?

> unmap_mapping_range() is already EXPORT_SYMBOL'd for this purpose
> (mm/memory.c), but without iomem_get_mapping() being exported, loadable
> modules cannot use it correctly for PCI BAR mappings, forcing ugly
> workarounds such as walking all process VMAs.

Well, we need to see the user(s) first, but once they materialize this
begs for a higher level API.  Until then it is moot anyway.