[PATCH mm-unstable v2 01/16] mm: Introduce generic_mmap_hint()

[Yang Shi]

On Wed, Dec 11, 2024 at 3:28 PM Kalesh Singh <kaleshsingh at google.com> wrote:
>
> Consolidate the hint searches from both directions (topdown and
> bottomup) into generic_mmap_hint().
>
> No functional change is introduced.
>
> Signed-off-by: Kalesh Singh <kaleshsingh at google.com>
> ---
>
> Changes in v2:
>   - MAP_FIXED case is also handled in arch_mmap_hint() since this is just a
>     special case of the hint addr being "enforced", per Yang Shi.
>   - Consolidate error handling in arch_mmap_hint().

Reviewed-by: Yang Shi <shy828301 at gmail.com>

>
>  include/linux/sched/mm.h |  4 +++
>  mm/mmap.c                | 76 ++++++++++++++++++++++++----------------
>  2 files changed, 50 insertions(+), 30 deletions(-)
>
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 928a626725e6..edeec19d1708 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -201,6 +201,10 @@ unsigned long mm_get_unmapped_area_vmflags(struct mm_struct *mm,
>                                            unsigned long flags,
>                                            vm_flags_t vm_flags);
>
> +unsigned long generic_mmap_hint(struct file *filp, unsigned long addr,
> +                               unsigned long len, unsigned long pgoff,
> +                               unsigned long flags);
> +
>  unsigned long
>  generic_get_unmapped_area(struct file *filp, unsigned long addr,
>                           unsigned long len, unsigned long pgoff,
> diff --git a/mm/mmap.c b/mm/mmap.c
> index df9154b15ef9..382b4eac5406 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -620,6 +620,47 @@ unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info)
>         return addr;
>  }
>
> +/*
> + * Look up unmapped area at the requested hint addr
> + *
> + * NOTE: MAP_FIXED is also handled here since it's a special case of
> + * enforcing the hint address.
> + *
> + * Returns:
> + *    ERR_VALUE: If the requested mapping is not valid
> + *    0: If there isn't a sufficiently large hole at the hint addr.
> + *    addr: If sufficient VA space is available at the hint address;
> + *          or MAP_FIXED was specified.
> + */
> +unsigned long generic_mmap_hint(struct file *filp, unsigned long addr,
> +                               unsigned long len, unsigned long pgoff,
> +                               unsigned long flags)
> +{
> +       struct mm_struct *mm = current->mm;
> +       struct vm_area_struct *vma, *prev;
> +       const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);
> +
> +       /* requested length too big for entire address space */
> +       if (len > mmap_end - mmap_min_addr)
> +               return -ENOMEM;
> +
> +       if (flags & MAP_FIXED)
> +               return addr;
> +
> +       if (!addr)
> +               return 0;
> +
> +       addr = PAGE_ALIGN(addr);
> +       vma = find_vma_prev(mm, addr, &prev);
> +       if (mmap_end - len >= addr && addr >= mmap_min_addr &&
> +           (!vma || addr + len <= vm_start_gap(vma)) &&
> +           (!prev || addr >= vm_end_gap(prev)))
> +               return addr;
> +
> +       /* Fallback to VA space search */
> +       return 0;
> +}
> +
>  /* Get an address range which is currently unmapped.
>   * For shmat() with addr=0.
>   *
> @@ -637,25 +678,13 @@ generic_get_unmapped_area(struct file *filp, unsigned long addr,
>                           unsigned long flags, vm_flags_t vm_flags)
>  {
>         struct mm_struct *mm = current->mm;
> -       struct vm_area_struct *vma, *prev;
>         struct vm_unmapped_area_info info = {};
>         const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);
>
> -       if (len > mmap_end - mmap_min_addr)
> -               return -ENOMEM;
> -
> -       if (flags & MAP_FIXED)
> +       addr = generic_mmap_hint(filp, addr, len, pgoff, flags);
> +       if (addr)
>                 return addr;
>
> -       if (addr) {
> -               addr = PAGE_ALIGN(addr);
> -               vma = find_vma_prev(mm, addr, &prev);
> -               if (mmap_end - len >= addr && addr >= mmap_min_addr &&
> -                   (!vma || addr + len <= vm_start_gap(vma)) &&
> -                   (!prev || addr >= vm_end_gap(prev)))
> -                       return addr;
> -       }
> -
>         info.length = len;
>         info.low_limit = mm->mmap_base;
>         info.high_limit = mmap_end;
> @@ -685,27 +714,14 @@ generic_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
>                                   unsigned long len, unsigned long pgoff,
>                                   unsigned long flags, vm_flags_t vm_flags)
>  {
> -       struct vm_area_struct *vma, *prev;
>         struct mm_struct *mm = current->mm;
>         struct vm_unmapped_area_info info = {};
>         const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);
>
> -       /* requested length too big for entire address space */
> -       if (len > mmap_end - mmap_min_addr)
> -               return -ENOMEM;
> -
> -       if (flags & MAP_FIXED)
> -               return addr;
> -
>         /* requesting a specific address */
> -       if (addr) {
> -               addr = PAGE_ALIGN(addr);
> -               vma = find_vma_prev(mm, addr, &prev);
> -               if (mmap_end - len >= addr && addr >= mmap_min_addr &&
> -                               (!vma || addr + len <= vm_start_gap(vma)) &&
> -                               (!prev || addr >= vm_end_gap(prev)))
> -                       return addr;
> -       }
> +       addr = generic_mmap_hint(filp, addr, len, pgoff, flags);
> +       if (addr)
> +               return addr;
>
>         info.flags = VM_UNMAPPED_AREA_TOPDOWN;
>         info.length = len;
> --
> 2.47.0.338.g60cca15819-goog
>
>