On Wed, Jul 10, 2024 at 03:22:43PM GMT, Liam R. Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
>
> Instead of zeroing the vma tree and then overwriting the area, let the
> area be overwritten and then clean up the gathered vmas using
> vms_complete_munmap_vmas().
>
> If a driver is mapping over an existing vma, then clear the ptes before
> the call_mmap() invocation. This is done using the vms_clear_ptes()
> helper.
>
> Temporarily keep track of the number of pages that will be removed and
> reduce the charged amount.
>
> This also drops the validate_mm() call in the vma_expand() function.
> It is necessary to drop the validate as it would fail since the mm
> map_count would be incorrect during a vma expansion, prior to the
> cleanup from vms_complete_munmap_vmas().
>
> Clean up the error handing of the vms_gather_munmap_vmas() by calling
> the verification within the function.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> ---
> mm/internal.h | 1 +
> mm/mmap.c | 80 +++++++++++++++++++++++++++------------------------
> 2 files changed, 44 insertions(+), 37 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index 11e90c6e5a3e..dd4eede1be0f 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -1503,6 +1503,7 @@ struct vma_munmap_struct {
> unsigned long stack_vm;
> unsigned long data_vm;
> bool unlock; /* Unlock after the munmap */
> + bool clear_ptes; /* If there are outstanding PTE to be cleared */
> };
>
> void __meminit __init_single_page(struct page *page, unsigned long pfn,
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 870c2d04ad6b..58cf42e22bfe 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -401,17 +401,21 @@ anon_vma_interval_tree_post_update_vma(struct vm_area_struct *vma)
> }
>
> static unsigned long count_vma_pages_range(struct mm_struct *mm,
> - unsigned long addr, unsigned long end)
> + 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;
> @@ -524,6 +528,7 @@ static inline void init_vma_munmap(struct vma_munmap_struct *vms,
> vms->exec_vm = vms->stack_vm = vms->data_vm = 0;
> vms->unmap_start = FIRST_USER_ADDRESS;
> vms->unmap_end = USER_PGTABLES_CEILING;
> + vms->clear_ptes = false; /* No PTEs to clear yet */
> }
>
> /*
> @@ -732,7 +737,6 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
> vma_iter_store(vmi, vma);
>
> vma_complete(&vp, vmi, vma->vm_mm);
> - validate_mm(vma->vm_mm);
> return 0;
>
> nomem:
> @@ -2606,11 +2610,14 @@ static inline void abort_munmap_vmas(struct ma_state *mas_detach)
> }
>
>
> -static void vms_complete_pte_clear(struct vma_munmap_struct *vms,
> +static inline void vms_clear_ptes(struct vma_munmap_struct *vms,
> struct ma_state *mas_detach, bool mm_wr_locked)
> {
> struct mmu_gather tlb;
>
> + if (!vms->clear_ptes) /* Nothing to do */
> + return;
> +
> /*
> * We can free page tables without write-locking mmap_lock because VMAs
> * were isolated before we downgraded mmap_lock.
> @@ -2624,6 +2631,7 @@ static void vms_complete_pte_clear(struct vma_munmap_struct *vms,
> /* start and end may be different if there is no prev or next vma. */
> free_pgtables(&tlb, mas_detach, vms->vma, vms->unmap_start, vms->unmap_end, mm_wr_locked);
> tlb_finish_mmu(&tlb);
> + vms->clear_ptes = false;
> }
>
> /*
> @@ -2647,7 +2655,7 @@ static void vms_complete_munmap_vmas(struct vma_munmap_struct *vms,
> if (vms->unlock)
> mmap_write_downgrade(mm);
>
> - vms_complete_pte_clear(vms, mas_detach, !vms->unlock);
> + vms_clear_ptes(vms, mas_detach, !vms->unlock);
> /* Update high watermark before we lower total_vm */
> update_hiwater_vm(mm);
> /* Stat accounting */
> @@ -2799,6 +2807,9 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
> while (vma_iter_addr(vms->vmi) > vms->start)
> vma_iter_prev_range(vms->vmi);
>
> + /* There are now PTEs that need to be cleared */
> + vms->clear_ptes = true;
> +
> return 0;
>
> userfaultfd_error:
> @@ -2807,6 +2818,7 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
> abort_munmap_vmas(mas_detach);
> start_split_failed:
> map_count_exceeded:
> + validate_mm(vms->mm);
I'm guessing here we know it's safe to validate?
> return error;
> }
>
> @@ -2851,8 +2863,8 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
>
> clear_tree_failed:
> abort_munmap_vmas(&mas_detach);
> -gather_failed:
> validate_mm(mm);
Additionally I imagine the gathering failing results in the tree being unable to
be validated?
> +gather_failed:
> return error;
> }
>
> @@ -2940,24 +2952,19 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> unsigned long merge_start = addr, merge_end = end;
> bool writable_file_mapping = false;
> pgoff_t vm_pgoff;
> - int error;
> + int error = -ENOMEM;
> VMA_ITERATOR(vmi, mm, addr);
> + unsigned long nr_pages, nr_accounted;
>
> - /* Check against address space limit. */
> - if (!may_expand_vm(mm, vm_flags, len >> PAGE_SHIFT)) {
> - unsigned long nr_pages;
> -
> - /*
> - * MAP_FIXED may remove pages of mappings that intersects with
> - * requested mapping. Account for the pages it would unmap.
> - */
> - nr_pages = count_vma_pages_range(mm, addr, end);
> -
> - if (!may_expand_vm(mm, vm_flags,
> - (len >> PAGE_SHIFT) - nr_pages))
> - return -ENOMEM;
> - }
> + 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, (len >> PAGE_SHIFT) - nr_pages))
> + return -ENOMEM;
>
> if (unlikely(!can_modify_mm(mm, addr, end)))
> return -EPERM;
> @@ -2974,18 +2981,13 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> mas_init(&mas_detach, &mt_detach, /* addr = */ 0);
> /* Prepare to unmap any existing mapping in the area */
> if (vms_gather_munmap_vmas(&vms, &mas_detach))
> - goto gather_failed;
> -
> - /* Remove any existing mappings from the vma tree */
> - if (vma_iter_clear_gfp(&vmi, addr, end, GFP_KERNEL))
> - goto clear_tree_failed;
> + return -ENOMEM;
>
> - /* Unmap any existing mapping in the area */
> - vms_complete_munmap_vmas(&vms, &mas_detach);
> next = vms.next;
> prev = vms.prev;
> vma = NULL;
> } else {
> + /* Minimal setup of vms */
Nit, but is this valid now we use the init function unconditionally?
> next = vma_next(&vmi);
> prev = vma_prev(&vmi);
> if (prev)
> @@ -2997,8 +2999,10 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> */
> if (accountable_mapping(file, vm_flags)) {
> charged = len >> PAGE_SHIFT;
> + charged -= nr_accounted;
> if (security_vm_enough_memory_mm(mm, charged))
> - return -ENOMEM;
> + goto abort_munmap;
> + vms.nr_accounted = 0;
> vm_flags |= VM_ACCOUNT;
> }
>
> @@ -3047,10 +3051,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> * not unmapped, but the maps are removed from the list.
> */
> vma = vm_area_alloc(mm);
> - if (!vma) {
> - error = -ENOMEM;
> + if (!vma)
> goto unacct_error;
> - }
>
> vma_iter_config(&vmi, addr, end);
> vma_set_range(vma, addr, end, pgoff);
> @@ -3059,6 +3061,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>
> if (file) {
> vma->vm_file = get_file(file);
> + /* call_mmap() may map PTE, so ensure there are no existing PTEs */
> + vms_clear_ptes(&vms, &mas_detach, true);
> error = call_mmap(file, vma);
> if (error)
> goto unmap_and_free_vma;
> @@ -3149,6 +3153,10 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> expanded:
> perf_event_mmap(vma);
>
> + /* Unmap any existing mapping in the area */
> + if (vms.nr_pages)
> + vms_complete_munmap_vmas(&vms, &mas_detach);
> +
> vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
> if (vm_flags & VM_LOCKED) {
> if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||
> @@ -3196,14 +3204,12 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> unacct_error:
> if (charged)
> vm_unacct_memory(charged);
> - validate_mm(mm);
> - return error;
>
> -clear_tree_failed:
> - abort_munmap_vmas(&mas_detach);
> -gather_failed:
> +abort_munmap:
> + if (vms.nr_pages)
> + abort_munmap_vmas(&mas_detach);
> validate_mm(mm);
> - return -ENOMEM;
> + return error;
> }
>
> static int __vm_munmap(unsigned long start, size_t len, bool unlock)
> --
> 2.43.0
>
Other than nits/queries, LGTM:
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
