[PATCH OLK-6.6 2/5] zcopy: Introduce the pageattach interface

14 Nov 2025

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/release-management/issues/ID3TGE

--------------------------------

Provide an efficient intra-node data transfer interface, enabling
applications to map the pages associated with a specified virtual
memory address space in the source process to the virtual address
space in the destination process.

Signed-off-by: Liu Mingrui <liumingrui@huawei.com>
---
 drivers/zcopy/zcopy.c | 671 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 670 insertions(+), 1 deletion(-)

diff --git a/drivers/zcopy/zcopy.c b/drivers/zcopy/zcopy.c
index 4e8657e07831..a65268b69491 100644
--- a/drivers/zcopy/zcopy.c
+++ b/drivers/zcopy/zcopy.c
@@ -7,6 +7,40 @@
 #include <linux/fs.h>
 #include <linux/cdev.h>
 #include <linux/uaccess.h>
+#include <linux/kallsyms.h>
+#include <linux/mm.h>
+#include <linux/kprobes.h>
+#include <linux/huge_mm.h>
+#include <linux/mm_types.h>
+#include <linux/mm_types_task.h>
+#include <linux/rmap.h>
+#include <linux/pgalloc.h>
+#include <asm-generic/pgalloc.h>
+#include <asm/tlbflush.h>
+#include <asm/pgtable-hwdef.h>
+
+#ifndef PUD_SHIFT
+#define ARM64_HW_PGTABLE_LEVEL_SHIFT(n) ((PAGE_SHIFT - 3) * (4 - (n)) + 3)
+#define PUD_SHIFT               ARM64_HW_PGTABLE_LEVEL_SHIFT(1)
+#endif
+
+enum pgt_entry {
+	NORMAL_PMD,
+	HPAGE_PMD,
+};
+
+enum {
+	IO_ATTACH	= 1,
+	IO_MAX
+};
+
+struct zcopy_ioctl_pswap {
+	unsigned long src_addr;
+	unsigned long dst_addr;
+	int src_pid;
+	int dst_pid;
+	unsigned long size;
+};
 
 struct zcopy_cdev {
 	struct cdev chrdev;
@@ -18,20 +52,655 @@ struct zcopy_cdev {
 
 static struct zcopy_cdev z_cdev;
 
-static long zcopy_ioctl(struct file *file, unsigned int type, unsigned long ptr)
+static pte_t *(*__zcopy_pte_offset_map)(pmd_t *, unsigned long, pmd_t *);
+static int (*__zcopy_pte_alloc)(struct mm_struct *, pmd_t *);
+static int (*__zcopy_pmd_alloc)(struct mm_struct *, pud_t *, unsigned long);
+static int (*__zcopy_pud_alloc)(struct mm_struct *, p4d_t *, unsigned long);
+static unsigned long (*kallsyms_lookup_name_funcp)(const char *);
+static void (*__zcopy_mmu_notifier_arch_invalidate_secondary_tlbs)(struct mm_struct *,
+					unsigned long, unsigned long);
+
+static struct kretprobe __kretprobe;
+
+static unsigned long __kprobe_lookup_name(const char *symbol_name)
+{
+	int ret;
+	void *addr;
+
+	__kretprobe.kp.symbol_name = symbol_name;
+	ret = register_kretprobe(&__kretprobe);
+	if (ret < 0) {
+		pr_err("register_kprobe failed, returned %d\n", ret);
+		return 0;
+	}
+	pr_info("Planted %s kprobe at %pK\n", symbol_name, __kretprobe.kp.addr);
+	addr = __kretprobe.kp.addr;
+	unregister_kretprobe(&__kretprobe);
+	return (unsigned long)addr;
+}
+
+static inline unsigned long __kallsyms_lookup_name(const char *symbol_name)
+{
+	if (kallsyms_lookup_name_funcp == NULL)
+		return 0;
+	return kallsyms_lookup_name_funcp(symbol_name);
+}
+
+static inline pud_t *zcopy_pud_alloc(struct mm_struct *mm, p4d_t *p4d,
+									unsigned long address)
+{
+	return (unlikely(p4d_none(*p4d)) &&
+		__zcopy_pud_alloc(mm, p4d, address)) ? NULL : pud_offset(p4d, address);
+}
+
+static inline pmd_t *zcopy_pmd_alloc(struct mm_struct *mm, pud_t *pud,
+						unsigned long address)
+{
+	return (unlikely(pud_none(*pud)) &&
+		__zcopy_pmd_alloc(mm, pud, address)) ? NULL : pmd_offset(pud, address);
+}
+
+static inline bool zcopy_pte_alloc(struct mm_struct *mm, pmd_t *pmd)
+{
+	return unlikely(pmd_none(*pmd)) && __zcopy_pte_alloc(mm, pmd);
+}
+
+static inline pte_t *zcopy_pte_offset_map(pmd_t *pmd, unsigned long addr)
+{
+	return __zcopy_pte_offset_map(pmd, addr, NULL);
+}
+
+static inline void zcopy_flush_tlb_mm_range(struct mm_struct *mm,
+				     unsigned long start, unsigned long end)
+{
+	unsigned long asid, pages;
+
+	start = round_down(start, PAGE_SIZE);
+	end = round_up(end, PAGE_SIZE);
+	pages = (end - start) >> PAGE_SHIFT;
+
+	if (__flush_tlb_range_limit_excess(start, end, pages, PAGE_SIZE)) {
+		dsb(ishst);
+		asid = __TLBI_VADDR(0, ASID(mm));
+		__tlbi(aside1is, asid);
+		__tlbi_user(aside1is, asid);
+		dsb(ish);
+		start = 0;
+		end = -1UL;
+		goto notifier;
+	}
+
+	dsb(ishst);
+	asid = ASID(mm);
+
+	__flush_tlb_range_op(vae1is, start, pages, PAGE_SIZE, asid, 0, true);
+
+notifier:
+	if (mm_has_notifiers(mm))
+		__zcopy_mmu_notifier_arch_invalidate_secondary_tlbs(mm, start, end);
+	dsb(ish);
+}
+
+static pud_t *zcopy_get_pud(struct mm_struct *mm, unsigned long addr)
+{
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+
+	pgd = pgd_offset(mm, addr);
+	if (pgd_none(*pgd))
+		return NULL;
+
+	p4d = p4d_offset(pgd, addr);
+	if (p4d_none(*p4d))
+		return NULL;
+
+	pud = pud_offset(p4d, addr);
+	if (pud_none(*pud))
+		return NULL;
+
+	return pud;
+}
+
+static pmd_t *zcopy_get_pmd(struct mm_struct *mm, unsigned long addr)
 {
+	pud_t *pud;
+	pmd_t *pmd;
+
+	pud = zcopy_get_pud(mm, addr);
+	if (!pud)
+		return NULL;
+
+	pmd = pmd_offset(pud, addr);
+	if (pmd_none(*pmd))
+		return NULL;
+
+	return pmd;
+}
+
+static pud_t *zcopy_alloc_new_pud(struct mm_struct *mm, unsigned long addr)
+{
+	pgd_t *pgd;
+	p4d_t *p4d;
+
+	pgd = pgd_offset(mm, addr);
+	p4d = p4d_alloc(mm, pgd, addr);
+	if (!p4d)
+		return NULL;
+
+	return zcopy_pud_alloc(mm, p4d, addr);
+}
+
+static pmd_t *zcopy_alloc_pmd(struct mm_struct *mm, unsigned long addr)
+{
+	pud_t *pud;
+	pmd_t *pmd;
+
+	pud = zcopy_alloc_new_pud(mm, addr);
+	if (!pud)
+		return NULL;
+
+	pmd = zcopy_pmd_alloc(mm, pud, addr);
+	if (!pmd)
+		return NULL;
+
+	return pmd;
+}
+
+static inline void zcopy_add_mm_counter(struct mm_struct *mm, int member, long value)
+{
+	struct percpu_counter *fbc = &mm->rss_stat[member];
+
+	if (percpu_counter_initialized(fbc))
+		percpu_counter_add(fbc, value);
+	else
+		percpu_counter_atomic_add(fbc, value);
+}
+
+static inline void zcopy_add_mm_rss_vec(struct mm_struct *mm, int *rss)
+{
+	int i;
+
+	if (current->mm == mm)
+		sync_mm_rss(mm);
+	for (i = 0; i < NR_MM_COUNTERS; i++)
+		if (rss[i])
+			zcopy_add_mm_counter(mm, i, rss[i]);
+}
+
+typedef int __bitwise fpb_t;
+#define FPB_IGNORE_DIRTY		((__force fpb_t)BIT(0))
+#define FPB_IGNORE_SOFT_DIRTY		((__force fpb_t)BIT(1))
+
+static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags)
+{
+	if (flags & FPB_IGNORE_DIRTY)
+		pte = pte_mkclean(pte);
+	if (likely(flags & FPB_IGNORE_SOFT_DIRTY))
+		pte = pte_clear_soft_dirty(pte);
+	return pte_wrprotect(pte_mkold(pte));
+}
+
+static inline bool vma_soft_dirty_enabled(struct vm_area_struct *vma)
+{
+	if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY))
+		return false;
+
+	return !(vma->vm_flags & VM_SOFTDIRTY);
+}
+
+static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
+		pte_t *start_ptep, pte_t pte, int max_nr, fpb_t flags)
+{
+	unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio);
+	const pte_t *end_ptep = start_ptep + max_nr;
+	pte_t expected_pte, *ptep;
+	int nr;
+
+	VM_WARN_ON_FOLIO(!pte_present(pte), folio);
+	VM_WARN_ON_FOLIO(!folio_test_large(folio) || max_nr < 1, folio);
+	VM_WARN_ON_FOLIO(page_folio(pfn_to_page(pte_pfn(pte))) != folio, folio);
+
+	nr = pte_batch_hint(start_ptep, pte);
+	expected_pte = __pte_batch_clear_ignored(pte_advance_pfn(pte, nr), flags);
+	ptep = start_ptep + nr;
+
+	while (ptep < end_ptep) {
+		pte = ptep_get(ptep);
+		pte = __pte_batch_clear_ignored(pte, flags);
+
+		if (!pte_same(pte, expected_pte))
+			break;
+
+		/*
+		 * Stop immediately once we reached the end of the folio. In
+		 * corner cases the next PFN might fall into a different folio.
+		 */
+		if (pte_pfn(pte) >= folio_end_pfn)
+			break;
+
+		nr = pte_batch_hint(ptep, pte);
+		expected_pte = pte_advance_pfn(expected_pte, nr);
+		ptep += nr;
+	}
+
+	return min(ptep - start_ptep, max_nr);
+}
+
+static __always_inline int zcopy_folio_try_dup_anon_rmap(struct folio *folio,
+		struct page *page, int nr_pages, struct vm_area_struct *src_vma,
+		enum rmap_level level)
+{
+	VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+	__folio_rmap_sanity_checks(folio, page, nr_pages, level);
+
+	switch (level) {
+	case RMAP_LEVEL_PTE:
+		if (!folio_test_large(folio)) {
+			if (PageAnonExclusive(page))
+				ClearPageAnonExclusive(page);
+			atomic_inc(&page->_mapcount);
+			break;
+		}
+
+		do {
+			if (PageAnonExclusive(page))
+				ClearPageAnonExclusive(page);
+			atomic_inc(&page->_mapcount);
+		} while (page++, --nr_pages > 0);
+		break;
+	case RMAP_LEVEL_PMD:
+		if (PageAnonExclusive(page))
+			ClearPageAnonExclusive(page);
+		atomic_inc(&folio->_entire_mapcount);
+		break;
+	}
 	return 0;
 }
 
+static int attach_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
+			pte_t *dst_ptep, pte_t *src_ptep, pte_t pte, unsigned long dst_addr,
+			unsigned long src_addr, int max_nr, int *rss)
+{
+	struct page *src_page;
+	struct folio *src_folio;
+	fpb_t flags = 0;
+	int nr;
+
+	src_page = pte_page(pte);
+	src_folio = page_folio(src_page);
+
+	if (unlikely(folio_test_large(src_folio) && max_nr != 1)) {
+		if (src_vma->vm_flags & VM_SHARED)
+			flags |= FPB_IGNORE_DIRTY;
+		if (!vma_soft_dirty_enabled(src_vma))
+			flags |= FPB_IGNORE_SOFT_DIRTY;
+
+		nr = folio_pte_batch(src_folio, src_addr, src_ptep, pte, max_nr, flags);
+
+		folio_ref_add(src_folio, nr);
+		if (unlikely(zcopy_folio_try_dup_anon_rmap(src_folio, src_page,
+							  nr, src_vma, RMAP_LEVEL_PTE))) {
+			folio_ref_sub(src_folio, nr);
+			return -EAGAIN;
+		}
+		rss[MM_ANONPAGES] += nr;
+		VM_WARN_ON_FOLIO(PageAnonExclusive(src_page), src_folio);
+
+		set_ptes(dst_vma->vm_mm, dst_addr, dst_ptep, pte, nr);
+		return nr;
+	}
+
+	folio_get(src_folio);
+	if (unlikely(zcopy_folio_try_dup_anon_rmap(src_folio, src_page,
+							1, src_vma, RMAP_LEVEL_PTE))) {
+		folio_put(src_folio);
+		return -EAGAIN;
+	}
+	rss[MM_ANONPAGES]++;
+	VM_WARN_ON_FOLIO(PageAnonExclusive(src_page), src_folio);
+
+	set_ptes(dst_vma->vm_mm, dst_addr, dst_ptep, pte, 1);
+	return 1;
+}
+
+static int attach_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
+			unsigned long dst_addr, unsigned long src_addr, pmd_t *dst_pmdp,
+			pmd_t *src_pmdp, unsigned long len)
+{
+	struct mm_struct *dst_mm = dst_vma->vm_mm;
+	pte_t *src_ptep, *dst_ptep, pte, dst_pte;
+	spinlock_t *dst_ptl;
+	int max_nr, ret, nr, i;
+	int rss[NR_MM_COUNTERS];
+	unsigned long src_addr_end = src_addr + len;
+
+	if (!vma_is_anonymous(dst_vma) || !vma_is_anonymous(src_vma)) {
+		pr_err("dst_vma is %d and src_vma is %d\n",
+			vma_is_anonymous(dst_vma), vma_is_anonymous(src_vma));
+		return -EINVAL;
+	}
+
+	memset(rss, 0, sizeof(int) * NR_MM_COUNTERS);
+
+	src_ptep = zcopy_pte_offset_map(src_pmdp, src_addr);
+	dst_ptep = zcopy_pte_offset_map(dst_pmdp, dst_addr);
+	dst_ptl = pte_lockptr(dst_mm, dst_pmdp);
+	spin_lock_nested(dst_ptl, SINGLE_DEPTH_NESTING);
+
+	do {
+		nr = 1;
+
+		/*
+		 * For special pte, there may not be corresponding page. Hence,
+		 * we skip this situation.
+		 */
+		pte = ptep_get(src_ptep);
+		if (pte_none(pte) || pte_special(pte) || !pte_present(pte))
+			continue;
+
+		max_nr = (src_addr_end - src_addr) / PAGE_SIZE;
+		/* check if there exists old mappings. */
+		for (i = 0; i < max_nr; i++) {
+			dst_pte = ptep_get(dst_ptep + i);
+			if (!pte_none(dst_pte)) {
+				ret = -EAGAIN;
+				goto out;
+			}
+		}
+
+		ret = attach_ptes(dst_vma, src_vma, dst_ptep, src_ptep, pte, dst_addr,
+							src_addr, max_nr, rss);
+		if (unlikely(ret == -EAGAIN))
+			goto out;
+
+		nr = ret;
+	} while (src_ptep += nr, src_addr += PAGE_SIZE * nr, dst_ptep += nr,
+		dst_addr += PAGE_SIZE * nr, src_addr != src_addr_end);
+
+	zcopy_flush_tlb_mm_range(dst_vma->vm_mm, dst_addr, dst_addr + len);
+	ret = 0;
+out:
+	zcopy_add_mm_rss_vec(dst_mm, rss);
+	spin_unlock(dst_ptl);
+	return ret;
+}
+
+static __always_inline unsigned long get_extent(enum pgt_entry entry,
+			unsigned long old_addr, unsigned long old_end,
+			unsigned long new_addr)
+{
+	unsigned long next, extent, mask, size;
+
+	switch (entry) {
+	case HPAGE_PMD:
+	case NORMAL_PMD:
+		mask = PMD_MASK;
+		size = PMD_SIZE;
+		break;
+	default:
+		BUILD_BUG();
+		break;
+	}
+
+	next = (old_addr + size) & mask;
+	/* even if next overflowed, extent below will be ok */
+	extent = next - old_addr;
+	if (extent > old_end - old_addr)
+		extent = old_end - old_addr;
+	next = (new_addr + size) & mask;
+	if (extent > next - new_addr)
+		extent = next - new_addr;
+	return extent;
+}
+
+static int attach_page_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+			unsigned long dst_addr, unsigned long src_addr, unsigned long size)
+{
+	struct vm_area_struct *src_vma, *dst_vma;
+	unsigned long extent, src_addr_end;
+	pmd_t *src_pmd, *dst_pmd;
+	int ret = 0;
+
+	src_addr_end = src_addr + size;
+	src_vma = find_vma(src_mm, src_addr);
+	dst_vma   = find_vma(dst_mm, dst_addr);
+	/* Check the vma has not been freed again.*/
+	if (!src_vma || !dst_vma)
+		return -ENOENT;
+
+	for (; src_addr < src_addr_end; src_addr += extent, dst_addr += extent) {
+		cond_resched();
+
+		extent = get_extent(NORMAL_PMD, src_addr, src_addr_end, dst_addr);
+		src_pmd = zcopy_get_pmd(src_mm, src_addr);
+		if (!src_pmd)
+			continue;
+		dst_pmd = zcopy_alloc_pmd(dst_mm, dst_addr);
+		if (!dst_pmd) {
+			ret = -ENOMEM;
+			break;
+		}
+
+		if (pmd_trans_huge(*src_pmd)) {
+			/* Not support hugepage mapping */
+			ret = -EOPNOTSUPP;
+			break;
+		} else if (is_swap_pmd(*src_pmd) || pmd_devmap(*src_pmd)) {
+			ret = -EOPNOTSUPP;
+			break;
+		}
+
+		if (zcopy_pte_alloc(dst_mm, dst_pmd)) {
+			ret = -ENOMEM;
+			break;
+		}
+
+		ret = attach_pte_range(dst_vma, src_vma, dst_addr, src_addr, dst_pmd,
+					src_pmd, PMD_SIZE);
+		if (ret < 0)
+			break;
+	}
+
+	return ret;
+}
+
+static int attach_pages(unsigned long dst_addr, unsigned long src_addr,
+					int dst_pid, int src_pid, unsigned long size)
+{
+	struct mm_struct *dst_mm, *src_mm;
+	struct task_struct *src_task, *dst_task;
+	struct page **process_pages;
+	unsigned long nr_pages;
+	unsigned int flags = 0;
+	int pinned_pages;
+	int locked = 1;
+	int ret;
+
+	ret = -EINVAL;
+	if (size <= 0)
+		goto out;
+
+	if ((src_addr & (PAGE_SIZE-1)) != 0 ||
+	    (dst_addr & (PAGE_SIZE-1)) != 0 ||
+	    (size & (PAGE_SIZE-1)) != 0) {
+		pr_err("Not aligned with PAGE_SIZE\n");
+		goto out;
+	}
+
+	/* check the addr is in userspace. wo do not allow */
+	if (!is_ttbr0_addr(dst_addr) || !is_ttbr0_addr(src_addr)) {
+		pr_err("Not allow kernelspace\n");
+		goto out;
+	}
+
+	ret = -ESRCH;
+	src_task = find_get_task_by_vpid(src_pid);
+	if (!src_task)
+		goto out;
+
+	src_mm = mm_access(src_task, PTRACE_MODE_ATTACH_REALCREDS);
+	if (!src_mm || IS_ERR(src_mm)) {
+		ret = IS_ERR(src_mm) ? PTR_ERR(src_mm) : -ESRCH;
+		if (ret == -EACCES)
+			ret = -EPERM;
+		goto put_src_task;
+	}
+
+	dst_task = find_get_task_by_vpid(dst_pid);
+	if (!dst_task)
+		goto put_src_mm;
+
+	dst_mm = mm_access(dst_task, PTRACE_MODE_ATTACH_REALCREDS);
+	if (!dst_mm || IS_ERR(dst_mm)) {
+		ret = IS_ERR(dst_mm) ? PTR_ERR(dst_mm) : -ESRCH;
+		if (ret == -EACCES)
+			ret = -EPERM;
+		goto put_dst_task;
+	}
+
+	if (src_mm == dst_mm) {
+		ret = -EINVAL;
+		pr_err("Attach is not allowed within the same address space");
+		goto put_dst_mm;
+	}
+
+	nr_pages = (src_addr + size - 1) / PAGE_SIZE - src_addr / PAGE_SIZE + 1;
+	process_pages = kvmalloc_array(nr_pages, sizeof(struct pages *), GFP_KERNEL);
+	if (!process_pages) {
+		ret = -ENOMEM;
+		goto put_dst_mm;
+	}
+
+	mmap_read_lock(src_mm);
+	pinned_pages = pin_user_pages_remote(src_mm, src_addr, nr_pages,
+					     flags, process_pages,
+					     &locked);
+	if (locked)
+		mmap_read_unlock(src_mm);
+
+	if (pinned_pages <= 0) {
+		ret = -EFAULT;
+		goto free_pages_array;
+	}
+
+	ret = attach_page_range(dst_mm, src_mm, dst_addr, src_addr, size);
+
+	unpin_user_pages_dirty_lock(process_pages, pinned_pages, 0);
+
+free_pages_array:
+	kvfree(process_pages);
+put_dst_mm:
+	mmput(dst_mm);
+put_dst_task:
+	put_task_struct(dst_task);
+put_src_mm:
+	mmput(src_mm);
+put_src_task:
+	put_task_struct(src_task);
+out:
+	return ret;
+}
+
+static long zcopy_ioctl(struct file *file, unsigned int type, unsigned long ptr)
+{
+	long ret = 0;
+
+	switch (type) {
+	case IO_ATTACH:
+	{
+		struct zcopy_ioctl_pswap ctx;
+
+		if (copy_from_user((void *)&ctx, (void *)ptr,
+								sizeof(struct zcopy_ioctl_pswap))) {
+			pr_err("copy from user for attach failed\n");
+			ret = -EFAULT;
+			break;
+		}
+		ret = attach_pages(ctx.dst_addr, ctx.src_addr, ctx.dst_pid,
+					ctx.src_pid, ctx.size);
+		break;
+	}
+	default:
+		break;
+	}
+
+	return ret;
+}
+
 static const struct file_operations zcopy_fops = {
 	.owner = THIS_MODULE,
 	.unlocked_ioctl = zcopy_ioctl,
 };
 
+#define REGISTER_CHECK(_var, _errstr) ({ \
+	int __ret = 0; \
+	if (!(_var)) { \
+		pr_warn("Not found %s\n", _errstr); \
+		__ret = -ENOENT; \
+	} \
+	__ret; \
+})
+
+static int register_unexport_func(void)
+{
+	int ret;
+
+	kallsyms_lookup_name_funcp
+		= (unsigned long (*)(const char *))__kprobe_lookup_name("kallsyms_lookup_name");
+	ret = REGISTER_CHECK(kallsyms_lookup_name_funcp, "kallsyms_lookup_name");
+	if (ret)
+		goto out;
+
+	__zcopy_pte_offset_map
+		= (pte_t *(*)(pmd_t *, unsigned long, pmd_t *))
+			__kallsyms_lookup_name("__pte_offset_map");
+	ret = REGISTER_CHECK(__zcopy_pte_offset_map, "__pte_offset_map");
+	if (ret)
+		goto out;
+
+	__zcopy_pte_alloc
+		= (int (*)(struct mm_struct *, pmd_t *))__kallsyms_lookup_name("__pte_alloc");
+	ret = REGISTER_CHECK(__zcopy_pte_alloc, "__pte_alloc");
+	if (ret)
+		goto out;
+
+	__zcopy_pmd_alloc
+		= (int (*)(struct mm_struct *, pud_t *, unsigned long))
+			__kallsyms_lookup_name("__pmd_alloc");
+	ret = REGISTER_CHECK(__zcopy_pmd_alloc, "__pmd_alloc");
+	if (ret)
+		goto out;
+
+	__zcopy_pud_alloc
+		= (int (*)(struct mm_struct *, p4d_t *, unsigned long))
+			__kallsyms_lookup_name("__pud_alloc");
+	ret = REGISTER_CHECK(__zcopy_pud_alloc, "__pud_alloc");
+	if (ret)
+		goto out;
+
+	__zcopy_mmu_notifier_arch_invalidate_secondary_tlbs
+		= (void (*)(struct mm_struct *, unsigned long, unsigned long))
+			__kallsyms_lookup_name("__mmu_notifier_arch_invalidate_secondary_tlbs");
+	ret = REGISTER_CHECK(__zcopy_mmu_notifier_arch_invalidate_secondary_tlbs,
+			"__mmu_notifier_arch_invalidate_secondary_tlbs");
+	if (ret)
+		goto out;
+
+out:
+	return ret;
+}
+
 static int register_device_zcopy(void)
 {
 	int ret;
 
+	ret = register_unexport_func();
+	if (ret) {
+		pr_err("register_unexport_func failed\n");
+		goto err_out;
+	}
+
 	ret = alloc_chrdev_region(&z_cdev.dev, 0, 1, "zcopy");
 	if (ret < 0) {
 		pr_err("alloc chrdev failed\n");
-- 
2.25.1

    