On Fri, Mar 26, 2021 at 06:55:03AM +0100, Christoph Hellwig wrote:

Add a helper that calls remap_pfn_range for an struct io_mapping, relying on the pgprot pre-validation done when creating the mapping instead of doing it at runtime.

Signed-off-by: Christoph Hellwig hch@lst.de

include/linux/io-mapping.h | 3 +++ mm/Kconfig | 3 +++ mm/Makefile | 1 + mm/io-mapping.c | 29 +++++++++++++++++++++++++++++ 4 files changed, 36 insertions(+) create mode 100644 mm/io-mapping.c

diff --git a/include/linux/io-mapping.h b/include/linux/io-mapping.h index c093e81310a9b3..e9743cfd858527 100644 --- a/include/linux/io-mapping.h +++ b/include/linux/io-mapping.h @@ -220,3 +220,6 @@ io_mapping_free(struct io_mapping *iomap) }

#endif /* _LINUX_IO_MAPPING_H */

+int io_mapping_map_user(struct io_mapping *iomap, struct vm_area_struct *vma,

• unsigned long addr, unsigned long pfn, unsigned long size);
  

I'm not sure what exactly brought me to check this, but while debugging I noticed this outside the header guard. But then after some more checks I saw nothing actually selects CONFIG_IO_MAPPING because commit using it was reverted in commit 0e4fe0c9f2f9 ("Revert "i915: use io_mapping_map_user"")

Is this something we want to re-attempt moving to mm/ ?

thanks Lucas De Marchi

diff --git a/mm/Kconfig b/mm/Kconfig index 24c045b24b9506..6b0f2cfbfac0f3 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -872,4 +872,7 @@ config MAPPING_DIRTY_HELPERS config KMAP_LOCAL bool

+# struct io_mapping based helper. Selected by drivers that need them +config IO_MAPPING

• bool

endmenu diff --git a/mm/Makefile b/mm/Makefile index 72227b24a61688..c0135e385984bb 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -120,3 +120,4 @@ obj-$(CONFIG_MEMFD_CREATE) += memfd.o obj-$(CONFIG_MAPPING_DIRTY_HELPERS) += mapping_dirty_helpers.o obj-$(CONFIG_PTDUMP_CORE) += ptdump.o obj-$(CONFIG_PAGE_REPORTING) += page_reporting.o +obj-$(CONFIG_IO_MAPPING) += io-mapping.o diff --git a/mm/io-mapping.c b/mm/io-mapping.c new file mode 100644 index 00000000000000..01b3627999304e --- /dev/null +++ b/mm/io-mapping.c @@ -0,0 +1,29 @@ +// 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;
  

• /* We rely on prevalidation of the io-mapping to skip track_pfn(). */
• return remap_pfn_range_notrack(vma, addr, pfn, size,

• __pgprot((pgprot_val(iomap->prot) & _PAGE_CACHE_MASK) |
  

• 	 (pgprot_val(vma->vm_page_prot) & ~_PAGE_CACHE_MASK)));
  

+}

+EXPORT_SYMBOL_GPL(io_mapping_map_user);

2.30.1

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