On Thu, 10 Dec 2015 19:21:42 -0800 Andy Lutomirski <luto@xxxxxxxxxx> wrote:
> From: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>
> Requiring special mappings to give a list of struct pages is
> inflexible: it prevents sane use of IO memory in a special mapping,
> it's inefficient (it requires arch code to initialize a list of
> struct pages, and it requires the mm core to walk the entire list
> just to figure out how long it is), and it prevents arch code from
> doing anything fancy when a special mapping fault occurs.
>
> Add a .fault method as an alternative to filling in a .pages array.
>
> ...
>
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -568,10 +568,27 @@ static inline void clear_tlb_flush_pending(struct mm_struct *mm)
> }
> #endif
>
> +struct vm_fault;
> +
> struct vm_special_mapping
> {
We may as well fix the code layout while we're in there.
> - const char *name;
> + const char *name; /* The name, e.g. "[vdso]". */
> +
> + /*
> + * If .fault is not provided, this is points to a
s/is//
> + * NULL-terminated array of pages that back the special mapping.
> + *
> + * This must not be NULL unless .fault is provided.
> + */
> struct page **pages;
> +
> + /*
> + * If non-NULL, then this is called to resolve page faults
> + * on the special mapping. If used, .pages is not checked.
> + */
> + int (*fault)(const struct vm_special_mapping *sm,
> + struct vm_area_struct *vma,
> + struct vm_fault *vmf);
> };
>
> enum tlb_flush_reason {
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 2ce04a649f6b..f717453b1a57 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3030,11 +3030,16 @@ static int special_mapping_fault(struct vm_area_struct *vma,
> pgoff_t pgoff;
> struct page **pages;
>
> - if (vma->vm_ops == &legacy_special_mapping_vmops)
> + if (vma->vm_ops == &legacy_special_mapping_vmops) {
> pages = vma->vm_private_data;
> - else
> - pages = ((struct vm_special_mapping *)vma->vm_private_data)->
> - pages;
> + } else {
> + struct vm_special_mapping *sm = vma->vm_private_data;
> +
> + if (sm->fault)
> + return sm->fault(sm, vma, vmf);
> +
> + pages = sm->pages;
> + }
>
> for (pgoff = vmf->pgoff; pgoff && *pages; ++pages)
> pgoff--;
Otherwise looks OK. I'll assume this will be merged via an x86 tree.
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