Hi Linus,
Poking my nose into this new helper,
> commit b4cbb197c7e7a68dbad0d491242e3ca67420c13e
> Author: Linus Torvalds <torva...@linux-foundation.org>
> Date: Tue Apr 16 13:45:37 2013 -0700
>
> vm: add vm_iomap_memory() helper function
[...]
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2393,6 +2393,53 @@ int remap_pfn_range(struct vm_area_struct *vma,
> unsigned long addr,
> }
> EXPORT_SYMBOL(remap_pfn_range);
>
> +/**
> + * vm_iomap_memory - remap memory to userspace
> + * @vma: user vma to map to
> + * @start: start of area
> + * @len: size of area
> + *
> + * This is a simplified io_remap_pfn_range() for common driver use. The
> + * driver just needs to give us the physical memory range to be mapped,
> + * we'll figure out the rest from the vma information.
> + *
> + * NOTE! Some drivers might want to tweak vma->vm_page_prot first to get
> + * whatever write-combining details or similar.
> + */
> +int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned
> long len)
> +{
> + unsigned long vm_len, pfn, pages;
> +
> + /* Check that the physical memory area passed in looks valid */
> + if (start + len < start)
is len == 0 accepted ?
> + return -EINVAL;
> + /*
> + * You *really* shouldn't map things that aren't page-aligned,
> + * but we've historically allowed it because IO memory might
> + * just have smaller alignment.
> + */
> + len += start & ~PAGE_MASK;
> + pfn = start >> PAGE_SHIFT;
> + pages = (len + ~PAGE_MASK) >> PAGE_SHIFT;
> + if (pfn + pages < pfn)
> + return -EINVAL;
> +
> + /* We start the mapping 'vm_pgoff' pages into the area */
> + if (vma->vm_pgoff > pages)
This seems to accept vma->vm_pgoff == pages, which would leave exactly 0
backing pages. Is this expected ?
> + return -EINVAL;
> + pfn += vma->vm_pgoff;
> + pages -= vma->vm_pgoff;
> +
> + /* Can we fit all of the mapping? */
> + vm_len = vma->vm_end - vma->vm_start;
> + if (vm_len >> PAGE_SHIFT > pages)
Is it possible that we get a situation where vm_end and vm_start are not
aligned on page addresses ? If it's allowed, then this test may succeed
even though the range requires more than "pages" backing pages. This
might be an issue since the first thing remap_pfn_range() does with its
"size" argument is to PAGE_ALIGN() it.
Thoughts ?
Thanks,
Mathieu
> + return -EINVAL;
> +
> + /* Ok, let it rip */
> + return io_remap_pfn_range(vma, vma->vm_start, pfn, vm_len,
> vma->vm_page_prot);
> +}
> +EXPORT_SYMBOL(vm_iomap_memory);
> +
> static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
> unsigned long addr, unsigned long end,
> pte_fn_t fn, void *data)
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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