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

["David Hildenbrand (Arm)" <david@kernel.org>]

On 5/11/26 18:16, 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. The link-down
> event is detected by the in-tree Xilinx DMA PL PCIe controller driver
> (drivers/pci/controller/pcie-xilinx-dma-pl.c), which notifies the endpoint
> driver via the link-down callback.
> 
> 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.
> 
> 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.

Okay, so you essentially want to implement something similar to revoke_iomem()?

-- 
Cheers,

David