// SPDX-License-Identifier: GPL-2.0-only
/*
 * mm/mmap.c
 *
 * Written by obz.
 *
 * Address space accounting code	<alan@lxorguk.ukuu.org.uk>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

/*
 * Official Linux v6.18: mm/mmap.c
 * https://github.com/torvalds/linux/blob/v6.18/mm/mmap.c#L1254
 * Complete upstream scope, not an elided book-code reconstruction.
 * See GPL-2.0.txt. Not a standalone translation unit.
 */

void exit_mmap(struct mm_struct *mm)
{
	struct mmu_gather tlb;
	struct vm_area_struct *vma;
	unsigned long nr_accounted = 0;
	VMA_ITERATOR(vmi, mm, 0);
	int count = 0;

	/* mm's last user has gone, and its about to be pulled down */
	mmu_notifier_release(mm);

	mmap_read_lock(mm);
	arch_exit_mmap(mm);

	vma = vma_next(&vmi);
	if (!vma || unlikely(xa_is_zero(vma))) {
		/* Can happen if dup_mmap() received an OOM */
		mmap_read_unlock(mm);
		mmap_write_lock(mm);
		goto destroy;
	}

	flush_cache_mm(mm);
	tlb_gather_mmu_fullmm(&tlb, mm);
	/* update_hiwater_rss(mm) here? but nobody should be looking */
	/* Use ULONG_MAX here to ensure all VMAs in the mm are unmapped */
	unmap_vmas(&tlb, &vmi.mas, vma, 0, ULONG_MAX, ULONG_MAX, false);
	mmap_read_unlock(mm);

	/*
	 * Set MMF_OOM_SKIP to hide this task from the oom killer/reaper
	 * because the memory has been already freed.
	 */
	mm_flags_set(MMF_OOM_SKIP, mm);
	mmap_write_lock(mm);
	mt_clear_in_rcu(&mm->mm_mt);
	vma_iter_set(&vmi, vma->vm_end);
	free_pgtables(&tlb, &vmi.mas, vma, FIRST_USER_ADDRESS,
		      USER_PGTABLES_CEILING, true);
	tlb_finish_mmu(&tlb);

	/*
	 * Walk the list again, actually closing and freeing it, with preemption
	 * enabled, without holding any MM locks besides the unreachable
	 * mmap_write_lock.
	 */
	vma_iter_set(&vmi, vma->vm_end);
	do {
		if (vma->vm_flags & VM_ACCOUNT)
			nr_accounted += vma_pages(vma);
		vma_mark_detached(vma);
		remove_vma(vma);
		count++;
		cond_resched();
		vma = vma_next(&vmi);
	} while (vma && likely(!xa_is_zero(vma)));

	BUG_ON(count != mm->map_count);

	trace_exit_mmap(mm);
destroy:
	__mt_destroy(&mm->mm_mt);
	mmap_write_unlock(mm);
	vm_unacct_memory(nr_accounted);
}