Re: [PATCH] mm: remove io-mapping

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

Sorry Andrew please ignore this for now, I'll send a v2 later.

I'm not having a great day here...

I wrongly assumed that, since this is wholly unused in practice, that nobody
would refer to it or include the header, but it turns out that's incorrect.

Thanks.

On Thu, Jul 24, 2025 at 03:53:12PM +0100, Lorenzo Stoakes wrote:
> This is dead code, which was used from commit b739f125e4eb ("i915: use
> io_mapping_map_user") but reverted a month later by commit
> 0e4fe0c9f2f9 ("Revert "i915: use io_mapping_map_user"") back in 2021.
>
> Since then nobody has used it, so remove it.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> ---
>  include/linux/io-mapping.h | 231 -------------------------------------
>  mm/Kconfig                 |   4 -
>  mm/Makefile                |   1 -
>  mm/io-mapping.c            |  30 -----
>  4 files changed, 266 deletions(-)
>  delete mode 100644 include/linux/io-mapping.h
>  delete mode 100644 mm/io-mapping.c
>
> diff --git a/include/linux/io-mapping.h b/include/linux/io-mapping.h
> deleted file mode 100644
> index 7376c1df9c90..000000000000
> --- a/include/linux/io-mapping.h
> +++ /dev/null
> @@ -1,231 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0-only */
> -/*
> - * Copyright © 2008 Keith Packard <keithp@keithp.com>
> - */
> -
> -#ifndef _LINUX_IO_MAPPING_H
> -#define _LINUX_IO_MAPPING_H
> -
> -#include <linux/types.h>
> -#include <linux/slab.h>
> -#include <linux/bug.h>
> -#include <linux/io.h>
> -#include <linux/pgtable.h>
> -#include <asm/page.h>
> -
> -/*
> - * The io_mapping mechanism provides an abstraction for mapping
> - * individual pages from an io device to the CPU in an efficient fashion.
> - *
> - * See Documentation/driver-api/io-mapping.rst
> - */
> -
> -struct io_mapping {
> -	resource_size_t base;
> -	unsigned long size;
> -	pgprot_t prot;
> -	void __iomem *iomem;
> -};
> -
> -#ifdef CONFIG_HAVE_ATOMIC_IOMAP
> -
> -#include <linux/pfn.h>
> -#include <asm/iomap.h>
> -/*
> - * For small address space machines, mapping large objects
> - * into the kernel virtual space isn't practical. Where
> - * available, use fixmap support to dynamically map pages
> - * of the object at run time.
> - */
> -
> -static inline struct io_mapping *
> -io_mapping_init_wc(struct io_mapping *iomap,
> -		   resource_size_t base,
> -		   unsigned long size)
> -{
> -	pgprot_t prot;
> -
> -	if (iomap_create_wc(base, size, &prot))
> -		return NULL;
> -
> -	iomap->base = base;
> -	iomap->size = size;
> -	iomap->prot = prot;
> -	return iomap;
> -}
> -
> -static inline void
> -io_mapping_fini(struct io_mapping *mapping)
> -{
> -	iomap_free(mapping->base, mapping->size);
> -}
> -
> -/* Atomic map/unmap */
> -static inline void __iomem *
> -io_mapping_map_atomic_wc(struct io_mapping *mapping,
> -			 unsigned long offset)
> -{
> -	resource_size_t phys_addr;
> -
> -	BUG_ON(offset >= mapping->size);
> -	phys_addr = mapping->base + offset;
> -	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
> -		preempt_disable();
> -	else
> -		migrate_disable();
> -	pagefault_disable();
> -	return __iomap_local_pfn_prot(PHYS_PFN(phys_addr), mapping->prot);
> -}
> -
> -static inline void
> -io_mapping_unmap_atomic(void __iomem *vaddr)
> -{
> -	kunmap_local_indexed((void __force *)vaddr);
> -	pagefault_enable();
> -	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
> -		preempt_enable();
> -	else
> -		migrate_enable();
> -}
> -
> -static inline void __iomem *
> -io_mapping_map_local_wc(struct io_mapping *mapping, unsigned long offset)
> -{
> -	resource_size_t phys_addr;
> -
> -	BUG_ON(offset >= mapping->size);
> -	phys_addr = mapping->base + offset;
> -	return __iomap_local_pfn_prot(PHYS_PFN(phys_addr), mapping->prot);
> -}
> -
> -static inline void io_mapping_unmap_local(void __iomem *vaddr)
> -{
> -	kunmap_local_indexed((void __force *)vaddr);
> -}
> -
> -static inline void __iomem *
> -io_mapping_map_wc(struct io_mapping *mapping,
> -		  unsigned long offset,
> -		  unsigned long size)
> -{
> -	resource_size_t phys_addr;
> -
> -	BUG_ON(offset >= mapping->size);
> -	phys_addr = mapping->base + offset;
> -
> -	return ioremap_wc(phys_addr, size);
> -}
> -
> -static inline void
> -io_mapping_unmap(void __iomem *vaddr)
> -{
> -	iounmap(vaddr);
> -}
> -
> -#else  /* HAVE_ATOMIC_IOMAP */
> -
> -#include <linux/uaccess.h>
> -
> -/* Create the io_mapping object*/
> -static inline struct io_mapping *
> -io_mapping_init_wc(struct io_mapping *iomap,
> -		   resource_size_t base,
> -		   unsigned long size)
> -{
> -	iomap->iomem = ioremap_wc(base, size);
> -	if (!iomap->iomem)
> -		return NULL;
> -
> -	iomap->base = base;
> -	iomap->size = size;
> -	iomap->prot = pgprot_writecombine(PAGE_KERNEL);
> -
> -	return iomap;
> -}
> -
> -static inline void
> -io_mapping_fini(struct io_mapping *mapping)
> -{
> -	iounmap(mapping->iomem);
> -}
> -
> -/* Non-atomic map/unmap */
> -static inline void __iomem *
> -io_mapping_map_wc(struct io_mapping *mapping,
> -		  unsigned long offset,
> -		  unsigned long size)
> -{
> -	return mapping->iomem + offset;
> -}
> -
> -static inline void
> -io_mapping_unmap(void __iomem *vaddr)
> -{
> -}
> -
> -/* Atomic map/unmap */
> -static inline void __iomem *
> -io_mapping_map_atomic_wc(struct io_mapping *mapping,
> -			 unsigned long offset)
> -{
> -	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
> -		preempt_disable();
> -	else
> -		migrate_disable();
> -	pagefault_disable();
> -	return io_mapping_map_wc(mapping, offset, PAGE_SIZE);
> -}
> -
> -static inline void
> -io_mapping_unmap_atomic(void __iomem *vaddr)
> -{
> -	io_mapping_unmap(vaddr);
> -	pagefault_enable();
> -	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
> -		preempt_enable();
> -	else
> -		migrate_enable();
> -}
> -
> -static inline void __iomem *
> -io_mapping_map_local_wc(struct io_mapping *mapping, unsigned long offset)
> -{
> -	return io_mapping_map_wc(mapping, offset, PAGE_SIZE);
> -}
> -
> -static inline void io_mapping_unmap_local(void __iomem *vaddr)
> -{
> -	io_mapping_unmap(vaddr);
> -}
> -
> -#endif /* !HAVE_ATOMIC_IOMAP */
> -
> -static inline struct io_mapping *
> -io_mapping_create_wc(resource_size_t base,
> -		     unsigned long size)
> -{
> -	struct io_mapping *iomap;
> -
> -	iomap = kmalloc(sizeof(*iomap), GFP_KERNEL);
> -	if (!iomap)
> -		return NULL;
> -
> -	if (!io_mapping_init_wc(iomap, base, size)) {
> -		kfree(iomap);
> -		return NULL;
> -	}
> -
> -	return iomap;
> -}
> -
> -static inline void
> -io_mapping_free(struct io_mapping *iomap)
> -{
> -	io_mapping_fini(iomap);
> -	kfree(iomap);
> -}
> -
> -int io_mapping_map_user(struct io_mapping *iomap, struct vm_area_struct *vma,
> -		unsigned long addr, unsigned long pfn, unsigned long size);
> -
> -#endif /* _LINUX_IO_MAPPING_H */
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 0287e8d94aea..b7a47bb593d6 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1254,10 +1254,6 @@ config KMAP_LOCAL
>  config KMAP_LOCAL_NON_LINEAR_PTE_ARRAY
>  	bool
>
> -# struct io_mapping based helper.  Selected by drivers that need them
> -config IO_MAPPING
> -	bool
> -
>  config MEMFD_CREATE
>  	bool "Enable memfd_create() system call" if EXPERT
>
> diff --git a/mm/Makefile b/mm/Makefile
> index 690ddcf7d9a1..e4ab5ca755d1 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -142,7 +142,6 @@ obj-$(CONFIG_MEMFD_CREATE) += memfd.o
>  obj-$(CONFIG_MAPPING_DIRTY_HELPERS) += mapping_dirty_helpers.o
>  obj-$(CONFIG_PTDUMP) += ptdump.o
>  obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o
> -obj-$(CONFIG_IO_MAPPING) += io-mapping.o
>  obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
>  obj-$(CONFIG_GENERIC_IOREMAP) += ioremap.o
>  obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o
> diff --git a/mm/io-mapping.c b/mm/io-mapping.c
> deleted file mode 100644
> index d3586e95c12c..000000000000
> --- a/mm/io-mapping.c
> +++ /dev/null
> @@ -1,30 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0-only
> -
> -#include <linux/mm.h>
> -#include <linux/io-mapping.h>
> -
> -/**
> - * io_mapping_map_user - remap an I/O mapping to userspace
> - * @iomap: the source io_mapping
> - * @vma: user vma to map to
> - * @addr: target user address to start at
> - * @pfn: physical address of kernel memory
> - * @size: size of map area
> - *
> - *  Note: this is only safe if the mm semaphore is held when called.
> - */
> -int io_mapping_map_user(struct io_mapping *iomap, struct vm_area_struct *vma,
> -		unsigned long addr, unsigned long pfn, unsigned long size)
> -{
> -	vm_flags_t expected_flags = VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
> -
> -	if (WARN_ON_ONCE((vma->vm_flags & expected_flags) != expected_flags))
> -		return -EINVAL;
> -
> -	pgprot_t remap_prot = __pgprot((pgprot_val(iomap->prot) & _PAGE_CACHE_MASK) |
> -				       (pgprot_val(vma->vm_page_prot) & ~_PAGE_CACHE_MASK));
> -
> -	/* We rely on prevalidation of the io-mapping to skip pfnmap tracking. */
> -	return remap_pfn_range_notrack(vma, addr, pfn, size, remap_prot);
> -}
> -EXPORT_SYMBOL_GPL(io_mapping_map_user);
> --
> 2.50.1
>