On Thu, Jul 04, 2024 at 02:27:18PM GMT, Liam R. Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
>
> The MAP_FIXED page count is available after the vms_gather_munmap_vmas()
> call, so use it instead of looping over the vmas twice.
Predictably indeed you removed the thing I commented on in the last patch
;) but at least this time I predicted it! ;)
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> ---
> mm/mmap.c | 36 ++++--------------------------------
> 1 file changed, 4 insertions(+), 32 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index b2de26683903..62edaabf3987 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -400,27 +400,6 @@ anon_vma_interval_tree_post_update_vma(struct vm_area_struct *vma)
> anon_vma_interval_tree_insert(avc, &avc->anon_vma->rb_root);
> }
>
> -static unsigned long count_vma_pages_range(struct mm_struct *mm,
> - unsigned long addr, unsigned long end,
> - unsigned long *nr_accounted)
> -{
> - VMA_ITERATOR(vmi, mm, addr);
> - struct vm_area_struct *vma;
> - unsigned long nr_pages = 0;
> -
> - *nr_accounted = 0;
> - for_each_vma_range(vmi, vma, end) {
> - unsigned long vm_start = max(addr, vma->vm_start);
> - unsigned long vm_end = min(end, vma->vm_end);
> -
> - nr_pages += PHYS_PFN(vm_end - vm_start);
> - if (vma->vm_flags & VM_ACCOUNT)
> - *nr_accounted += PHYS_PFN(vm_end - vm_start);
> - }
> -
> - return nr_pages;
> -}
> -
> static void __vma_link_file(struct vm_area_struct *vma,
> struct address_space *mapping)
> {
> @@ -2946,17 +2925,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> pgoff_t vm_pgoff;
> int error = -ENOMEM;
> VMA_ITERATOR(vmi, mm, addr);
> - unsigned long nr_pages, nr_accounted;
> -
> - nr_pages = count_vma_pages_range(mm, addr, end, &nr_accounted);
> -
> - /* Check against address space limit. */
> - /*
> - * MAP_FIXED may remove pages of mappings that intersects with requested
> - * mapping. Account for the pages it would unmap.
> - */
> - if (!may_expand_vm(mm, vm_flags, pglen - nr_pages))
> - return -ENOMEM;
>
> if (unlikely(!can_modify_mm(mm, addr, end)))
> return -EPERM;
> @@ -2987,6 +2955,10 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> vma_iter_next_range(&vmi);
> }
>
> + /* Check against address space limit. */
> + if (!may_expand_vm(mm, vm_flags, pglen - vms.nr_pages))
> + goto abort_munmap;
> +
I know you can literally only do this after the vms_gather_munmap_vmas(),
but this does change where we check this, so for instance we do
arch_unmap() without having checked may_expand_vm().
However I assume this is fine?
> /*
> * Private writable mapping: check memory availability
> */
> --
> 2.43.0
>
Looks good to me generally,
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
