include/linux/userfaultfd_k.h

/* SPDX-License-Identifier: GPL-2.0 */
/*
 *  include/linux/userfaultfd_k.h
 *
 *  Copyright (C) 2015  Red Hat, Inc.
 *
 */

#ifndef _LINUX_USERFAULTFD_K_H
#define _LINUX_USERFAULTFD_K_H

#ifdef CONFIG_USERFAULTFD

#include <linux/userfaultfd.h> /* linux/include/uapi/linux/userfaultfd.h */

#include <linux/fcntl.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/leafops.h>
#include <asm-generic/pgtable_uffd.h>
#include <linux/hugetlb_inline.h>

/* The set of all possible UFFD-related VM flags. */
#define __VM_UFFD_FLAGS (VM_UFFD_MISSING | VM_UFFD_MINOR | \
			 VM_UFFD_WP | VM_UFFD_RWP)

#define __VMA_UFFD_FLAGS mk_vma_flags_from_masks(VMA_UFFD_MISSING, VMA_UFFD_WP, \
						 VMA_UFFD_MINOR, VMA_UFFD_RWP)

/*
 * CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining
 * new flags, since they might collide with O_* ones. We want
 * to re-use O_* flags that couldn't possibly have a meaning
 * from userfaultfd, in order to leave a free define-space for
 * shared O_* flags.
 */
#define UFFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK)

/*
 * Start with fault_pending_wqh and fault_wqh so they're more likely
 * to be in the same cacheline.
 *
 * Locking order:
 *	fd_wqh.lock
 *		fault_pending_wqh.lock
 *			fault_wqh.lock
 *		event_wqh.lock
 *
 * To avoid deadlocks, IRQs must be disabled when taking any of the above locks,
 * since fd_wqh.lock is taken by aio_poll() while it's holding a lock that's
 * also taken in IRQ context.
 */
struct userfaultfd_ctx {
	/* waitqueue head for the pending (i.e. not read) userfaults */
	wait_queue_head_t fault_pending_wqh;
	/* waitqueue head for the userfaults */
	wait_queue_head_t fault_wqh;
	/* waitqueue head for the pseudo fd to wakeup poll/read */
	wait_queue_head_t fd_wqh;
	/* waitqueue head for events */
	wait_queue_head_t event_wqh;
	/* a refile sequence protected by fault_pending_wqh lock */
	seqcount_spinlock_t refile_seq;
	/* pseudo fd refcounting */
	refcount_t refcount;
	/* userfaultfd syscall flags */
	unsigned int flags;
	/* features requested from the userspace */
	unsigned int features;
	/* released */
	bool released;
	/*
	 * Prevents userfaultfd operations (fill/move/wp) from happening while
	 * some non-cooperative event(s) is taking place. Increments are done
	 * in write-mode. Whereas, userfaultfd operations, which includes
	 * reading mmap_changing, is done under read-mode.
	 */
	struct rw_semaphore map_changing_lock;
	/* memory mappings are changing because of non-cooperative event */
	atomic_t mmap_changing;
	/* mm with one ore more vmas attached to this userfaultfd_ctx */
	struct mm_struct *mm;
};

extern vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason);

/* VMA userfaultfd operations */
struct vm_uffd_ops {
	/* Checks if a VMA can support userfaultfd */
	bool (*can_userfault)(struct vm_area_struct *vma, vm_flags_t vm_flags);
	/*
	 * Called to resolve UFFDIO_CONTINUE request.
	 * Should return the folio found at pgoff in the VMA's pagecache if it
	 * exists or ERR_PTR otherwise.
	 * The returned folio is locked and with reference held.
	 */
	struct folio *(*get_folio_noalloc)(struct inode *inode, pgoff_t pgoff);
	/*
	 * Called during resolution of UFFDIO_COPY request.
	 * Should allocate and return a folio or NULL if allocation fails.
	 */
	struct folio *(*alloc_folio)(struct vm_area_struct *vma,
				     unsigned long addr);
	/*
	 * Called during resolution of UFFDIO_COPY request.
	 * Should only be called with a folio returned by alloc_folio() above.
	 * The folio will be set to locked.
	 * Returns 0 on success, error code on failure.
	 */
	int (*filemap_add)(struct folio *folio, struct vm_area_struct *vma,
			 unsigned long addr);
	/*
	 * Called during resolution of UFFDIO_COPY request on the error
	 * handling path.
	 * Should revert the operation of ->filemap_add().
	 */
	void (*filemap_remove)(struct folio *folio, struct vm_area_struct *vma);
};

/* A combined operation mode + behavior flags. */
typedef unsigned int __bitwise uffd_flags_t;

/* Mutually exclusive modes of operation. */
enum mfill_atomic_mode {
	MFILL_ATOMIC_COPY,
	MFILL_ATOMIC_ZEROPAGE,
	MFILL_ATOMIC_CONTINUE,
	MFILL_ATOMIC_POISON,
	NR_MFILL_ATOMIC_MODES,
};

#define MFILL_ATOMIC_MODE_BITS (const_ilog2(NR_MFILL_ATOMIC_MODES - 1) + 1)
#define MFILL_ATOMIC_BIT(nr) BIT(MFILL_ATOMIC_MODE_BITS + (nr))
#define MFILL_ATOMIC_FLAG(nr) ((__force uffd_flags_t) MFILL_ATOMIC_BIT(nr))
#define MFILL_ATOMIC_MODE_MASK ((__force uffd_flags_t) (MFILL_ATOMIC_BIT(0) - 1))

static inline bool uffd_flags_mode_is(uffd_flags_t flags, enum mfill_atomic_mode expected)
{
	return (flags & MFILL_ATOMIC_MODE_MASK) == ((__force uffd_flags_t) expected);
}

static inline uffd_flags_t uffd_flags_set_mode(uffd_flags_t flags, enum mfill_atomic_mode mode)
{
	flags &= ~MFILL_ATOMIC_MODE_MASK;
	return flags | ((__force uffd_flags_t) mode);
}

/* Flags controlling behavior. These behavior changes are mode-independent. */
#define MFILL_ATOMIC_WP MFILL_ATOMIC_FLAG(0)

extern long uffd_wp_range(struct vm_area_struct *vma,
			  unsigned long start, unsigned long len, bool enable_wp);
extern int mrwprotect_range(struct userfaultfd_ctx *ctx, unsigned long start,
			    unsigned long len, bool enable_rwp);

/* move_pages */
void double_pt_lock(spinlock_t *ptl1, spinlock_t *ptl2);
void double_pt_unlock(spinlock_t *ptl1, spinlock_t *ptl2);
int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pmd_t dst_pmdval,
			struct vm_area_struct *dst_vma,
			struct vm_area_struct *src_vma,
			unsigned long dst_addr, unsigned long src_addr);

/* mm helpers */
static inline bool is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma,
					struct vm_userfaultfd_ctx vm_ctx)
{
	return vma->vm_userfaultfd_ctx.ctx == vm_ctx.ctx;
}

/*
 * Never enable huge pmd sharing on some uffd registered vmas:
 *
 * - VM_UFFD_WP and VM_UFFD_RWP VMAs, because the write protect / access
 *   tracking information is per pgtable entry.
 *
 * - VM_UFFD_MINOR VMAs, because otherwise we would never get minor faults for
 *   VMAs which share huge pmds. (If you have two mappings to the same
 *   underlying pages, and fault in the non-UFFD-registered one with a write,
 *   with huge pmd sharing this would *also* setup the second UFFD-registered
 *   mapping, and we'd not get minor faults.)
 */
static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma)
{
	return vma_test_any_mask(vma,
		mk_vma_flags_from_masks(VMA_UFFD_WP, VMA_UFFD_RWP,
					VMA_UFFD_MINOR));
}

/*
 * Don't do fault around for WP, RWP or MINOR registered uffd range.  For
 * MINOR registered range, fault around will be a total disaster and ptes can
 * be installed without notifications; for WP it should mostly be fine as long
 * as the fault around checks for pte_none() before the installation, however
 * to be super safe we just forbid it; for RWP, pre-faulted neighbours would
 * be indistinguishable from accessed pages in PAGEMAP_SCAN (PAGE_IS_ACCESSED)
 * and pollute the tracked working set, so each page must be populated by its
 * own fault.
 */
static inline bool uffd_disable_fault_around(struct vm_area_struct *vma)
{
	return vma_test_any_mask(vma,
		mk_vma_flags_from_masks(VMA_UFFD_WP, VMA_UFFD_RWP,
					VMA_UFFD_MINOR));
}

static inline bool userfaultfd_missing(struct vm_area_struct *vma)
{
	return vma_test_any_mask(vma, VMA_UFFD_MISSING);
}

static inline bool userfaultfd_wp(struct vm_area_struct *vma)
{
	return vma_test_any_mask(vma, VMA_UFFD_WP);
}

static inline bool userfaultfd_minor(struct vm_area_struct *vma)
{
	return vma_test_any_mask(vma, VMA_UFFD_MINOR);
}

static inline bool userfaultfd_rwp(struct vm_area_struct *vma)
{
	/*
	 * Callers gate PAGE_NONE usage on this; PAGE_NONE is a BUILD_BUG()
	 * without CONFIG_ARCH_HAS_PTE_PROTNONE, so fold to false.
	 */
	if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_PROTNONE))
		return false;
	return vma_test_single_mask(vma, VMA_UFFD_RWP);
}

static inline bool userfaultfd_protected(struct vm_area_struct *vma)
{
	return userfaultfd_wp(vma) || userfaultfd_rwp(vma);
}

static inline bool userfaultfd_pte_wp(struct vm_area_struct *vma,
				      pte_t pte)
{
	return userfaultfd_wp(vma) && pte_uffd(pte);
}

static inline bool userfaultfd_huge_pmd_wp(struct vm_area_struct *vma,
					   pmd_t pmd)
{
	return userfaultfd_wp(vma) && pmd_uffd(pmd);
}

static inline bool userfaultfd_pte_rwp(struct vm_area_struct *vma,
				       pte_t pte)
{
	return userfaultfd_rwp(vma) && pte_uffd(pte);
}

static inline bool userfaultfd_huge_pmd_rwp(struct vm_area_struct *vma,
					    pmd_t pmd)
{
	return userfaultfd_rwp(vma) && pmd_uffd(pmd);
}

static inline bool userfaultfd_armed(struct vm_area_struct *vma)
{
	return vma_test_any_mask(vma, __VMA_UFFD_FLAGS);
}

static inline bool vma_has_uffd_without_event_remap(struct vm_area_struct *vma)
{
	struct userfaultfd_ctx *uffd_ctx = vma->vm_userfaultfd_ctx.ctx;

	return uffd_ctx && (uffd_ctx->features & UFFD_FEATURE_EVENT_REMAP) == 0;
}

extern int dup_userfaultfd(struct vm_area_struct *, struct list_head *);
extern void dup_userfaultfd_complete(struct list_head *);
void dup_userfaultfd_fail(struct list_head *);

extern void mremap_userfaultfd_prep(struct vm_area_struct *,
				    struct vm_userfaultfd_ctx *);
extern void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *,
					unsigned long from, unsigned long to,
					unsigned long len);
void mremap_userfaultfd_fail(struct vm_userfaultfd_ctx *);

extern bool userfaultfd_remove(struct vm_area_struct *vma,
			       unsigned long start,
			       unsigned long end);

extern int userfaultfd_unmap_prep(struct vm_area_struct *vma,
		unsigned long start, unsigned long end, struct list_head *uf);
extern void userfaultfd_unmap_complete(struct mm_struct *mm,
				       struct list_head *uf);
extern bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma);
extern bool userfaultfd_wp_async(struct vm_area_struct *vma);
extern bool userfaultfd_rwp_async(struct vm_area_struct *vma);

static inline bool userfaultfd_wp_use_markers(struct vm_area_struct *vma)
{
	/* Only wr-protect mode uses pte markers */
	if (!userfaultfd_wp(vma))
		return false;

	/* File-based uffd-wp always need markers */
	if (!vma_is_anonymous(vma))
		return true;

	/*
	 * Anonymous uffd-wp only needs the markers if WP_UNPOPULATED
	 * enabled (to apply markers on zero pages).
	 */
	return userfaultfd_wp_unpopulated(vma);
}

/*
 * Returns true if this swap pte carries uffd-tracked state in either
 * form (pte marker or a normal swap pte), false otherwise.
 */
static inline bool pte_swp_uffd_any(pte_t pte)
{
	if (!uffd_supports_wp_marker())
		return false;

	if (pte_present(pte))
		return false;

	if (pte_swp_uffd(pte))
		return true;

	if (pte_is_uffd_wp_marker(pte))
		return true;

	return false;
}
#else /* CONFIG_USERFAULTFD */

/* mm helpers */
static inline vm_fault_t handle_userfault(struct vm_fault *vmf,
				unsigned long reason)
{
	return VM_FAULT_SIGBUS;
}

static inline long uffd_wp_range(struct vm_area_struct *vma,
				 unsigned long start, unsigned long len,
				 bool enable_wp)
{
	return false;
}

static inline bool is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma,
					struct vm_userfaultfd_ctx vm_ctx)
{
	return true;
}

static inline bool userfaultfd_missing(struct vm_area_struct *vma)
{
	return false;
}

static inline bool userfaultfd_wp(struct vm_area_struct *vma)
{
	return false;
}

static inline bool userfaultfd_minor(struct vm_area_struct *vma)
{
	return false;
}

static inline bool userfaultfd_rwp(struct vm_area_struct *vma)
{
	return false;
}

static inline bool userfaultfd_protected(struct vm_area_struct *vma)
{
	return false;
}

static inline bool userfaultfd_pte_wp(struct vm_area_struct *vma,
				      pte_t pte)
{
	return false;
}

static inline bool userfaultfd_huge_pmd_wp(struct vm_area_struct *vma,
					   pmd_t pmd)
{
	return false;
}

static inline bool userfaultfd_pte_rwp(struct vm_area_struct *vma,
				       pte_t pte)
{
	return false;
}

static inline bool userfaultfd_huge_pmd_rwp(struct vm_area_struct *vma,
					    pmd_t pmd)
{
	return false;
}

static inline bool userfaultfd_armed(struct vm_area_struct *vma)
{
	return false;
}

static inline int dup_userfaultfd(struct vm_area_struct *vma,
				  struct list_head *l)
{
	return 0;
}

static inline void dup_userfaultfd_complete(struct list_head *l)
{
}

static inline void dup_userfaultfd_fail(struct list_head *l)
{
}

static inline void mremap_userfaultfd_prep(struct vm_area_struct *vma,
					   struct vm_userfaultfd_ctx *ctx)
{
}

static inline void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *ctx,
					       unsigned long from,
					       unsigned long to,
					       unsigned long len)
{
}

static inline void mremap_userfaultfd_fail(struct vm_userfaultfd_ctx *ctx)
{
}

static inline bool userfaultfd_remove(struct vm_area_struct *vma,
				      unsigned long start,
				      unsigned long end)
{
	return true;
}

static inline int userfaultfd_unmap_prep(struct vm_area_struct *vma,
					 unsigned long start, unsigned long end,
					 struct list_head *uf)
{
	return 0;
}

static inline void userfaultfd_unmap_complete(struct mm_struct *mm,
					      struct list_head *uf)
{
}

static inline bool uffd_disable_fault_around(struct vm_area_struct *vma)
{
	return false;
}

static inline bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma)
{
	return false;
}

static inline bool userfaultfd_wp_async(struct vm_area_struct *vma)
{
	return false;
}

static inline bool userfaultfd_rwp_async(struct vm_area_struct *vma)
{
	return false;
}

static inline bool vma_has_uffd_without_event_remap(struct vm_area_struct *vma)
{
	return false;
}

static inline bool userfaultfd_wp_use_markers(struct vm_area_struct *vma)
{
	return false;
}

/*
 * Returns true if this swap pte carries uffd-tracked state in either
 * form (pte marker or a normal swap pte), false otherwise.
 */
static inline bool pte_swp_uffd_any(pte_t pte)
{
	return false;
}
#endif /* CONFIG_USERFAULTFD */
#endif /* _LINUX_USERFAULTFD_K_H */