Re: [PATCH v11 2/3] mm: add a field to store names for private anonymous memory

[Suren Baghdasaryan]

On Tue, Oct 19, 2021 at 2:55 PM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
>
> From: Colin Cross <ccross@xxxxxxxxxx>
>
> In many userspace applications, and especially in VM based applications
> like Android uses heavily, there are multiple different allocators in use.
> At a minimum there is libc malloc and the stack, and in many cases there
> are libc malloc, the stack, direct syscalls to mmap anonymous memory, and
> multiple VM heaps (one for small objects, one for big objects, etc.).
> Each of these layers usually has its own tools to inspect its usage;
> malloc by compiling a debug version, the VM through heap inspection tools,
> and for direct syscalls there is usually no way to track them.
>
> On Android we heavily use a set of tools that use an extended version of
> the logic covered in Documentation/vm/pagemap.txt to walk all pages mapped
> in userspace and slice their usage by process, shared (COW) vs.  unique
> mappings, backing, etc.  This can account for real physical memory usage
> even in cases like fork without exec (which Android uses heavily to share
> as many private COW pages as possible between processes), Kernel SamePage
> Merging, and clean zero pages.  It produces a measurement of the pages
> that only exist in that process (USS, for unique), and a measurement of
> the physical memory usage of that process with the cost of shared pages
> being evenly split between processes that share them (PSS).
>
> If all anonymous memory is indistinguishable then figuring out the real
> physical memory usage (PSS) of each heap requires either a pagemap walking
> tool that can understand the heap debugging of every layer, or for every
> layer's heap debugging tools to implement the pagemap walking logic, in
> which case it is hard to get a consistent view of memory across the whole
> system.
>
> Tracking the information in userspace leads to all sorts of problems.
> It either needs to be stored inside the process, which means every
> process has to have an API to export its current heap information upon
> request, or it has to be stored externally in a filesystem that
> somebody needs to clean up on crashes.  It needs to be readable while
> the process is still running, so it has to have some sort of
> synchronization with every layer of userspace.  Efficiently tracking
> the ranges requires reimplementing something like the kernel vma
> trees, and linking to it from every layer of userspace.  It requires
> more memory, more syscalls, more runtime cost, and more complexity to
> separately track regions that the kernel is already tracking.
>
> This patch adds a field to /proc/pid/maps and /proc/pid/smaps to show a
> userspace-provided name for anonymous vmas.  The names of named anonymous
> vmas are shown in /proc/pid/maps and /proc/pid/smaps as [anon:<name>].
>
> Userspace can set the name for a region of memory by calling
> prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, start, len, (unsigned long)name);
> Setting the name to NULL clears it. The name length limit is 80 bytes
> including NUL-terminator and is checked to contain only printable ascii
> characters (including space), except '[',']','\','$' and '`'. Ascii
> strings are being used to have a descriptive identifiers for vmas, which
> can be understood by the users reading /proc/pid/maps or /proc/pid/smaps.
> Names can be standardized for a given system and they can include some
> variable parts such as the name of the allocator or a library, tid of
> the thread using it, etc.
>
> The name is stored in a pointer in the shared union in vm_area_struct
> that points to a null terminated string. Anonymous vmas with the same
> name (equivalent strings) and are otherwise mergeable will be merged.
> The name pointers are not shared between vmas even if they contain the
> same name. The name pointer is stored in a union with fields that are
> only used on file-backed mappings, so it does not increase memory usage.
>
> CONFIG_ANON_VMA_NAME kernel configuration is introduced to enable this
> feature. It keeps the feature disabled by default to prevent any
> additional memory overhead and to avoid confusing procfs parsers on
> systems which are not ready to support named anonymous vmas.
>
> The patch is based on the original patch developed by Colin Cross, more
> specifically on its latest version [1] posted upstream by Sumit Semwal.
> It used a userspace pointer to store vma names. In that design, name
> pointers could be shared between vmas. However during the last upstreaming
> attempt, Kees Cook raised concerns [2] about this approach and suggested
> to copy the name into kernel memory space, perform validity checks [3]
> and store as a string referenced from vm_area_struct.
> One big concern is about fork() performance which would need to strdup
> anonymous vma names. Dave Hansen suggested experimenting with worst-case
> scenario of forking a process with 64k vmas having longest possible names
> [4]. I ran this experiment on an ARM64 Android device and recorded a
> worst-case regression of almost 40% when forking such a process. This
> regression is addressed in the followup patch which replaces the pointer
> to a name with a refcounted structure that allows sharing the name pointer
> between vmas of the same name. Instead of duplicating the string during
> fork() or when splitting a vma it increments the refcount.
>
> [1] https://lore.kernel.org/linux-mm/20200901161459.11772-4-sumit.semwal@xxxxxxxxxx/
> [2] https://lore.kernel.org/linux-mm/202009031031.D32EF57ED@keescook/
> [3] https://lore.kernel.org/linux-mm/202009031022.3834F692@keescook/
> [4] https://lore.kernel.org/linux-mm/5d0358ab-8c47-2f5f-8e43-23b89d6a8e95@xxxxxxxxx/
>
> Changes for prctl(2) manual page (in the options section):
>
> PR_SET_VMA
>         Sets an attribute specified in arg2 for virtual memory areas
>         starting from the address specified in arg3 and spanning the
>         size specified  in arg4. arg5 specifies the value of the attribute
>         to be set. Note that assigning an attribute to a virtual memory
>         area might prevent it from being merged with adjacent virtual
>         memory areas due to the difference in that attribute's value.
>
>         Currently, arg2 must be one of:
>
>         PR_SET_VMA_ANON_NAME
>                 Set a name for anonymous virtual memory areas. arg5 should
>                 be a pointer to a null-terminated string containing the
>                 name. The name length including null byte cannot exceed
>                 80 bytes. If arg5 is NULL, the name of the appropriate
>                 anonymous virtual memory areas will be reset. The name
>                 can contain only printable ascii characters (including
>                 space), except '[',']','\','$' and '`'.
>
>                 This feature is available only if the kernel is built with
>                 the CONFIG_ANON_VMA_NAME option enabled.

As Andrew suggested, I checked the image sizes with allnoconfig builds:

unpatched Linus' ToT
   text    data     bss     dec     hex filename
1324759      32   73928 1398719 1557bf vmlinux

After the first patch is applied (madvise refactoring)
   text    data     bss     dec     hex filename
1322346      32   73928 1396306 154e52 vmlinux
>>> 2413 bytes decrease vs ToT <<<

After all patches applied with CONFIG_ANON_VMA_NAME=n
   text    data     bss     dec     hex filename
1322337      32   73928 1396297 154e49 vmlinux
>>> 2422 bytes decrease vs ToT <<<

After all patches applied with CONFIG_ANON_VMA_NAME=y
   text    data     bss     dec     hex filename
1325228      32   73928 1399188 155994 vmlinux
>>> 469 bytes increase vs ToT <<<

>
> Signed-off-by: Colin Cross <ccross@xxxxxxxxxx>
> [surenb: rebased over v5.15-rc6, replaced userpointer with a kernel copy,
> added input sanitization and CONFIG_ANON_VMA_NAME config. The bulk of the
> work here was done by Colin Cross, therefore, with his permission, keeping
> him as the author]
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> previous version at:
> https://lore.kernel.org/all/20211001205657.815551-2-surenb@xxxxxxxxxx/
>
> changes in v11
> - Introduced CONFIG_ANON_VMA_NAME, per Andrew Morton
> - Amended patch description to explain the reason for string names,
> per Michal Hocko
> - Fixed build error when CONFIG_ADVISE_SYSCALLS=n, per kernel test robot
>
>  Documentation/filesystems/proc.rst |   2 +
>  fs/proc/task_mmu.c                 |  12 ++-
>  fs/userfaultfd.c                   |   7 +-
>  include/linux/mm.h                 |  13 ++-
>  include/linux/mm_types.h           |  64 +++++++++++++-
>  include/uapi/linux/prctl.h         |   3 +
>  kernel/fork.c                      |   2 +
>  kernel/sys.c                       |  63 ++++++++++++++
>  mm/Kconfig                         |  14 ++++
>  mm/madvise.c                       | 129 ++++++++++++++++++++++++++++-
>  mm/mempolicy.c                     |   3 +-
>  mm/mlock.c                         |   2 +-
>  mm/mmap.c                          |  38 +++++----
>  mm/mprotect.c                      |   2 +-
>  14 files changed, 322 insertions(+), 32 deletions(-)
>
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 042c418f4090..a067eec54ef1 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -431,6 +431,8 @@ is not associated with a file:
>   [stack]                    the stack of the main process
>   [vdso]                     the "virtual dynamic shared object",
>                              the kernel system call handler
> +[anon:<name>]               an anonymous mapping that has been
> +                            named by userspace
>   =======                    ====================================
>
>   or if empty, the mapping is anonymous.
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index cf25be3e0321..809e794dc0c5 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -308,6 +308,8 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
>
>         name = arch_vma_name(vma);
>         if (!name) {
> +               const char *anon_name;
> +
>                 if (!mm) {
>                         name = "[vdso]";
>                         goto done;
> @@ -319,8 +321,16 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
>                         goto done;
>                 }
>
> -               if (is_stack(vma))
> +               if (is_stack(vma)) {
>                         name = "[stack]";
> +                       goto done;
> +               }
> +
> +               anon_name = vma_anon_name(vma);
> +               if (anon_name) {
> +                       seq_pad(m, ' ');
> +                       seq_printf(m, "[anon:%s]", anon_name);
> +               }
>         }
>
>  done:
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 22bf14ab2d16..5b2af7b82776 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -877,7 +877,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
>                                  new_flags, vma->anon_vma,
>                                  vma->vm_file, vma->vm_pgoff,
>                                  vma_policy(vma),
> -                                NULL_VM_UFFD_CTX);
> +                                NULL_VM_UFFD_CTX, vma_anon_name(vma));
>                 if (prev)
>                         vma = prev;
>                 else
> @@ -1436,7 +1436,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
>                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
>                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
>                                  vma_policy(vma),
> -                                ((struct vm_userfaultfd_ctx){ ctx }));
> +                                ((struct vm_userfaultfd_ctx){ ctx }),
> +                                vma_anon_name(vma));
>                 if (prev) {
>                         vma = prev;
>                         goto next;
> @@ -1613,7 +1614,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
>                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
>                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
>                                  vma_policy(vma),
> -                                NULL_VM_UFFD_CTX);
> +                                NULL_VM_UFFD_CTX, vma_anon_name(vma));
>                 if (prev) {
>                         vma = prev;
>                         goto next;
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 73a52aba448f..4fb8e0095f35 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2548,7 +2548,7 @@ static inline int vma_adjust(struct vm_area_struct *vma, unsigned long start,
>  extern struct vm_area_struct *vma_merge(struct mm_struct *,
>         struct vm_area_struct *prev, unsigned long addr, unsigned long end,
>         unsigned long vm_flags, struct anon_vma *, struct file *, pgoff_t,
> -       struct mempolicy *, struct vm_userfaultfd_ctx);
> +       struct mempolicy *, struct vm_userfaultfd_ctx, const char *);
>  extern struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *);
>  extern int __split_vma(struct mm_struct *, struct vm_area_struct *,
>         unsigned long addr, int new_below);
> @@ -3284,5 +3284,16 @@ static inline int seal_check_future_write(int seals, struct vm_area_struct *vma)
>         return 0;
>  }
>
> +#ifdef CONFIG_ANON_VMA_NAME
> +int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> +                         unsigned long len_in, const char *name);
> +#else
> +static inline int
> +madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> +                     unsigned long len_in, const char *name) {
> +       return 0;
> +}
> +#endif
> +
>  #endif /* __KERNEL__ */
>  #endif /* _LINUX_MM_H */
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 7f8ee09c711f..3ad85843e924 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -350,11 +350,19 @@ struct vm_area_struct {
>         /*
>          * For areas with an address space and backing store,
>          * linkage into the address_space->i_mmap interval tree.
> +        *
> +        * For private anonymous mappings, a pointer to a null terminated string
> +        * containing the name given to the vma, or NULL if unnamed.
>          */
> -       struct {
> -               struct rb_node rb;
> -               unsigned long rb_subtree_last;
> -       } shared;
> +
> +       union {
> +               struct {
> +                       struct rb_node rb;
> +                       unsigned long rb_subtree_last;
> +               } shared;
> +               /* Serialized by mmap_sem. */
> +               char *anon_name;
> +       };
>
>         /*
>          * A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma
> @@ -809,4 +817,52 @@ typedef struct {
>         unsigned long val;
>  } swp_entry_t;
>
> +#ifdef CONFIG_ANON_VMA_NAME
> +/*
> + * mmap_lock should be read-locked when calling vma_anon_name() and while using
> + * the returned pointer.
> + */
> +extern const char *vma_anon_name(struct vm_area_struct *vma);
> +
> +/*
> + * mmap_lock should be read-locked for orig_vma->vm_mm.
> + * mmap_lock should be write-locked for new_vma->vm_mm or new_vma should be
> + * isolated.
> + */
> +extern void dup_vma_anon_name(struct vm_area_struct *orig_vma,
> +                             struct vm_area_struct *new_vma);
> +
> +/*
> + * mmap_lock should be write-locked or vma should have been isolated under
> + * write-locked mmap_lock protection.
> + */
> +extern void free_vma_anon_name(struct vm_area_struct *vma);
> +
> +/* mmap_lock should be read-locked */
> +static inline bool is_same_vma_anon_name(struct vm_area_struct *vma,
> +                                        const char *name)
> +{
> +       const char *vma_name = vma_anon_name(vma);
> +
> +       /* either both NULL, or pointers to same string */
> +       if (vma_name == name)
> +               return true;
> +
> +       return name && vma_name && !strcmp(name, vma_name);
> +}
> +#else /* CONFIG_ANON_VMA_NAME */
> +static inline const char *vma_anon_name(struct vm_area_struct *vma)
> +{
> +       return NULL;
> +}
> +static inline void dup_vma_anon_name(struct vm_area_struct *orig_vma,
> +                             struct vm_area_struct *new_vma) {}
> +static inline void free_vma_anon_name(struct vm_area_struct *vma) {}
> +static inline bool is_same_vma_anon_name(struct vm_area_struct *vma,
> +                                        const char *name)
> +{
> +       return true;
> +}
> +#endif  /* CONFIG_ANON_VMA_NAME */
> +
>  #endif /* _LINUX_MM_TYPES_H */
> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index 43bd7f713c39..4c8cbf510b2d 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -269,4 +269,7 @@ struct prctl_mm_map {
>  # define PR_SCHED_CORE_SHARE_FROM      3 /* pull core_sched cookie to pid */
>  # define PR_SCHED_CORE_MAX             4
>
> +#define PR_SET_VMA             0x53564d41
> +# define PR_SET_VMA_ANON_NAME          0
> +
>  #endif /* _LINUX_PRCTL_H */
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 38681ad44c76..bb7ac41048c2 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -366,12 +366,14 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
>                 *new = data_race(*orig);
>                 INIT_LIST_HEAD(&new->anon_vma_chain);
>                 new->vm_next = new->vm_prev = NULL;
> +               dup_vma_anon_name(orig, new);
>         }
>         return new;
>  }
>
>  void vm_area_free(struct vm_area_struct *vma)
>  {
> +       free_vma_anon_name(vma);
>         kmem_cache_free(vm_area_cachep, vma);
>  }
>
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 8fdac0d90504..2450a9f33cb0 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2261,6 +2261,66 @@ int __weak arch_prctl_spec_ctrl_set(struct task_struct *t, unsigned long which,
>
>  #define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE)
>
> +#ifdef CONFIG_ANON_VMA_NAME
> +
> +#define ANON_VMA_NAME_MAX_LEN          80
> +#define ANON_VMA_NAME_INVALID_CHARS    "\\`$[]"
> +
> +static inline bool is_valid_name_char(char ch)
> +{
> +       /* printable ascii characters, excluding ANON_VMA_NAME_INVALID_CHARS */
> +       return ch > 0x1f && ch < 0x7f &&
> +               !strchr(ANON_VMA_NAME_INVALID_CHARS, ch);
> +}
> +
> +static int prctl_set_vma(unsigned long opt, unsigned long addr,
> +                        unsigned long size, unsigned long arg)
> +{
> +       struct mm_struct *mm = current->mm;
> +       const char __user *uname;
> +       char *name, *pch;
> +       int error;
> +
> +       switch (opt) {
> +       case PR_SET_VMA_ANON_NAME:
> +               uname = (const char __user *)arg;
> +               if (uname) {
> +                       name = strndup_user(uname, ANON_VMA_NAME_MAX_LEN);
> +
> +                       if (IS_ERR(name))
> +                               return PTR_ERR(name);
> +
> +                       for (pch = name; *pch != '\0'; pch++) {
> +                               if (!is_valid_name_char(*pch)) {
> +                                       kfree(name);
> +                                       return -EINVAL;
> +                               }
> +                       }
> +               } else {
> +                       /* Reset the name */
> +                       name = NULL;
> +               }
> +
> +               mmap_write_lock(mm);
> +               error = madvise_set_anon_name(mm, addr, size, name);
> +               mmap_write_unlock(mm);
> +               kfree(name);
> +               break;
> +       default:
> +               error = -EINVAL;
> +       }
> +
> +       return error;
> +}
> +
> +#else /* CONFIG_ANON_VMA_NAME */
> +static int prctl_set_vma(unsigned long opt, unsigned long start,
> +                        unsigned long size, unsigned long arg)
> +{
> +       return -EINVAL;
> +}
> +#endif /* CONFIG_ANON_VMA_NAME */
> +
>  SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>                 unsigned long, arg4, unsigned long, arg5)
>  {
> @@ -2530,6 +2590,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>                 error = sched_core_share_pid(arg2, arg3, arg4, arg5);
>                 break;
>  #endif
> +       case PR_SET_VMA:
> +               error = prctl_set_vma(arg2, arg3, arg4, arg5);
> +               break;
>         default:
>                 error = -EINVAL;
>                 break;
> diff --git a/mm/Kconfig b/mm/Kconfig
> index d16ba9249bc5..e6340469f8ff 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -894,6 +894,20 @@ config IO_MAPPING
>  config SECRETMEM
>         def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED
>
> +config ANON_VMA_NAME
> +       bool "Anonymous VMA name support"
> +       depends on PROC_FS && ADVISE_SYSCALLS && MMU
> +
> +       help
> +         Allow naming anonymous virtual memory areas.
> +
> +         This feature allows assigning names to virtual memory areas. Assigned
> +         names can be later retrieved from /proc/pid/maps and /proc/pid/smaps
> +         and help identifying individual anonymous memory areas.
> +         Assigning a name to anonymous virtual memory area might prevent that
> +         area from being merged with adjacent virtual memory areas due to the
> +         difference in their name.
> +
>  source "mm/damon/Kconfig"
>
>  endmenu
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 224f971b2da2..948fad92ba1b 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -18,6 +18,7 @@
>  #include <linux/fadvise.h>
>  #include <linux/sched.h>
>  #include <linux/sched/mm.h>
> +#include <linux/string.h>
>  #include <linux/uio.h>
>  #include <linux/ksm.h>
>  #include <linux/fs.h>
> @@ -62,19 +63,84 @@ static int madvise_need_mmap_write(int behavior)
>         }
>  }
>
> +#ifdef CONFIG_ANON_VMA_NAME
> +static inline bool has_vma_anon_name(struct vm_area_struct *vma)
> +{
> +       return !vma->vm_file && vma->anon_name;
> +}
> +
> +const char *vma_anon_name(struct vm_area_struct *vma)
> +{
> +       if (!has_vma_anon_name(vma))
> +               return NULL;
> +
> +       mmap_assert_locked(vma->vm_mm);
> +
> +       return vma->anon_name;
> +}
> +
> +void dup_vma_anon_name(struct vm_area_struct *orig_vma,
> +                      struct vm_area_struct *new_vma)
> +{
> +       if (!has_vma_anon_name(orig_vma))
> +               return;
> +
> +       new_vma->anon_name = kstrdup(orig_vma->anon_name, GFP_KERNEL);
> +}
> +
> +void free_vma_anon_name(struct vm_area_struct *vma)
> +{
> +       if (!has_vma_anon_name(vma))
> +               return;
> +
> +       kfree(vma->anon_name);
> +       vma->anon_name = NULL;
> +}
> +
> +/* mmap_lock should be write-locked */
> +static int replace_vma_anon_name(struct vm_area_struct *vma, const char *name)
> +{
> +       if (!name) {
> +               free_vma_anon_name(vma);
> +               return 0;
> +       }
> +
> +       if (vma->anon_name) {
> +               /* Same name, nothing to do here */
> +               if (!strcmp(name, vma->anon_name))
> +                       return 0;
> +
> +               free_vma_anon_name(vma);
> +       }
> +       vma->anon_name = kstrdup(name, GFP_KERNEL);
> +       if (!vma->anon_name)
> +               return -ENOMEM;
> +
> +       return 0;
> +}
> +#else /* CONFIG_ANON_VMA_NAME */
> +static int replace_vma_anon_name(struct vm_area_struct *vma, const char *name)
> +{
> +       if (name)
> +               return -EINVAL;
> +
> +       return 0;
> +}
> +#endif /* CONFIG_ANON_VMA_NAME */
>  /*
>   * Update the vm_flags on region of a vma, splitting it or merging it as
>   * necessary.  Must be called with mmap_sem held for writing;
>   */
>  static int madvise_update_vma(struct vm_area_struct *vma,
>                               struct vm_area_struct **prev, unsigned long start,
> -                             unsigned long end, unsigned long new_flags)
> +                             unsigned long end, unsigned long new_flags,
> +                             const char *name)
>  {
>         struct mm_struct *mm = vma->vm_mm;
>         int error;
>         pgoff_t pgoff;
>
> -       if (new_flags == vma->vm_flags) {
> +       if (new_flags == vma->vm_flags && is_same_vma_anon_name(vma, name)) {
>                 *prev = vma;
>                 return 0;
>         }
> @@ -82,7 +148,7 @@ static int madvise_update_vma(struct vm_area_struct *vma,
>         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
>         *prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,
>                           vma->vm_file, pgoff, vma_policy(vma),
> -                         vma->vm_userfaultfd_ctx);
> +                         vma->vm_userfaultfd_ctx, name);
>         if (*prev) {
>                 vma = *prev;
>                 goto success;
> @@ -111,6 +177,11 @@ static int madvise_update_vma(struct vm_area_struct *vma,
>          * vm_flags is protected by the mmap_lock held in write mode.
>          */
>         vma->vm_flags = new_flags;
> +       if (!vma->vm_file) {
> +               error = replace_vma_anon_name(vma, name);
> +               if (error)
> +                       return error;
> +       }
>
>         return 0;
>  }
> @@ -938,7 +1009,8 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
>                 break;
>         }
>
> -       error = madvise_update_vma(vma, prev, start, end, new_flags);
> +       error = madvise_update_vma(vma, prev, start, end, new_flags,
> +                                  vma_anon_name(vma));
>
>  out:
>         /*
> @@ -1118,6 +1190,55 @@ int madvise_walk_vmas(struct mm_struct *mm, unsigned long start,
>         return unmapped_error;
>  }
>
> +#ifdef CONFIG_ANON_VMA_NAME
> +static int madvise_vma_anon_name(struct vm_area_struct *vma,
> +                                struct vm_area_struct **prev,
> +                                unsigned long start, unsigned long end,
> +                                unsigned long name)
> +{
> +       int error;
> +
> +       /* Only anonymous mappings can be named */
> +       if (vma->vm_file)
> +               return -EBADF;
> +
> +       error = madvise_update_vma(vma, prev, start, end, vma->vm_flags,
> +                                  (const char *)name);
> +
> +       /*
> +        * madvise() returns EAGAIN if kernel resources, such as
> +        * slab, are temporarily unavailable.
> +        */
> +       if (error == -ENOMEM)
> +               error = -EAGAIN;
> +       return error;
> +}
> +
> +int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> +                         unsigned long len_in, const char *name)
> +{
> +       unsigned long end;
> +       unsigned long len;
> +
> +       if (start & ~PAGE_MASK)
> +               return -EINVAL;
> +       len = (len_in + ~PAGE_MASK) & PAGE_MASK;
> +
> +       /* Check to see whether len was rounded up from small -ve to zero */
> +       if (len_in && !len)
> +               return -EINVAL;
> +
> +       end = start + len;
> +       if (end < start)
> +               return -EINVAL;
> +
> +       if (end == start)
> +               return 0;
> +
> +       return madvise_walk_vmas(mm, start, end, (unsigned long)name,
> +                                madvise_vma_anon_name);
> +}
> +#endif /* CONFIG_ANON_VMA_NAME */
>  /*
>   * The madvise(2) system call.
>   *
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index d12e0608fced..3cca13ea0a34 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -810,7 +810,8 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
>                         ((vmstart - vma->vm_start) >> PAGE_SHIFT);
>                 prev = vma_merge(mm, prev, vmstart, vmend, vma->vm_flags,
>                                  vma->anon_vma, vma->vm_file, pgoff,
> -                                new_pol, vma->vm_userfaultfd_ctx);
> +                                new_pol, vma->vm_userfaultfd_ctx,
> +                                vma_anon_name(vma));
>                 if (prev) {
>                         vma = prev;
>                         next = vma->vm_next;
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 16d2ee160d43..c878515680af 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -511,7 +511,7 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
>         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
>         *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
>                           vma->vm_file, pgoff, vma_policy(vma),
> -                         vma->vm_userfaultfd_ctx);
> +                         vma->vm_userfaultfd_ctx, vma_anon_name(vma));
>         if (*prev) {
>                 vma = *prev;
>                 goto success;
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 88dcc5c25225..4375ee8b1926 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1029,7 +1029,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
>   */
>  static inline int is_mergeable_vma(struct vm_area_struct *vma,
>                                 struct file *file, unsigned long vm_flags,
> -                               struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
> +                               struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
> +                               const char *anon_name)
>  {
>         /*
>          * VM_SOFTDIRTY should not prevent from VMA merging, if we
> @@ -1047,6 +1048,8 @@ static inline int is_mergeable_vma(struct vm_area_struct *vma,
>                 return 0;
>         if (!is_mergeable_vm_userfaultfd_ctx(vma, vm_userfaultfd_ctx))
>                 return 0;
> +       if (!is_same_vma_anon_name(vma, anon_name))
> +               return 0;
>         return 1;
>  }
>
> @@ -1079,9 +1082,10 @@ static int
>  can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
>                      struct anon_vma *anon_vma, struct file *file,
>                      pgoff_t vm_pgoff,
> -                    struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
> +                    struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
> +                    const char *anon_name)
>  {
> -       if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx) &&
> +       if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name) &&
>             is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
>                 if (vma->vm_pgoff == vm_pgoff)
>                         return 1;
> @@ -1100,9 +1104,10 @@ static int
>  can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
>                     struct anon_vma *anon_vma, struct file *file,
>                     pgoff_t vm_pgoff,
> -                   struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
> +                   struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
> +                   const char *anon_name)
>  {
> -       if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx) &&
> +       if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name) &&
>             is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
>                 pgoff_t vm_pglen;
>                 vm_pglen = vma_pages(vma);
> @@ -1113,9 +1118,9 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
>  }
>
>  /*
> - * Given a mapping request (addr,end,vm_flags,file,pgoff), figure out
> - * whether that can be merged with its predecessor or its successor.
> - * Or both (it neatly fills a hole).
> + * Given a mapping request (addr,end,vm_flags,file,pgoff,anon_name),
> + * figure out whether that can be merged with its predecessor or its
> + * successor.  Or both (it neatly fills a hole).
>   *
>   * In most cases - when called for mmap, brk or mremap - [addr,end) is
>   * certain not to be mapped by the time vma_merge is called; but when
> @@ -1160,7 +1165,8 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
>                         unsigned long end, unsigned long vm_flags,
>                         struct anon_vma *anon_vma, struct file *file,
>                         pgoff_t pgoff, struct mempolicy *policy,
> -                       struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
> +                       struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
> +                       const char *anon_name)
>  {
>         pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
>         struct vm_area_struct *area, *next;
> @@ -1190,7 +1196,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
>                         mpol_equal(vma_policy(prev), policy) &&
>                         can_vma_merge_after(prev, vm_flags,
>                                             anon_vma, file, pgoff,
> -                                           vm_userfaultfd_ctx)) {
> +                                           vm_userfaultfd_ctx, anon_name)) {
>                 /*
>                  * OK, it can.  Can we now merge in the successor as well?
>                  */
> @@ -1199,7 +1205,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
>                                 can_vma_merge_before(next, vm_flags,
>                                                      anon_vma, file,
>                                                      pgoff+pglen,
> -                                                    vm_userfaultfd_ctx) &&
> +                                                    vm_userfaultfd_ctx, anon_name) &&
>                                 is_mergeable_anon_vma(prev->anon_vma,
>                                                       next->anon_vma, NULL)) {
>                                                         /* cases 1, 6 */
> @@ -1222,7 +1228,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
>                         mpol_equal(policy, vma_policy(next)) &&
>                         can_vma_merge_before(next, vm_flags,
>                                              anon_vma, file, pgoff+pglen,
> -                                            vm_userfaultfd_ctx)) {
> +                                            vm_userfaultfd_ctx, anon_name)) {
>                 if (prev && addr < prev->vm_end)        /* case 4 */
>                         err = __vma_adjust(prev, prev->vm_start,
>                                          addr, prev->vm_pgoff, NULL, next);
> @@ -1755,7 +1761,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>          * Can we just expand an old mapping?
>          */
>         vma = vma_merge(mm, prev, addr, addr + len, vm_flags,
> -                       NULL, file, pgoff, NULL, NULL_VM_UFFD_CTX);
> +                       NULL, file, pgoff, NULL, NULL_VM_UFFD_CTX, NULL);
>         if (vma)
>                 goto out;
>
> @@ -1804,7 +1810,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>                  */
>                 if (unlikely(vm_flags != vma->vm_flags && prev)) {
>                         merge = vma_merge(mm, prev, vma->vm_start, vma->vm_end, vma->vm_flags,
> -                               NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX);
> +                               NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX, NULL);
>                         if (merge) {
>                                 /* ->mmap() can change vma->vm_file and fput the original file. So
>                                  * fput the vma->vm_file here or we would add an extra fput for file
> @@ -3057,7 +3063,7 @@ static int do_brk_flags(unsigned long addr, unsigned long len, unsigned long fla
>
>         /* Can we just expand an old private anonymous mapping? */
>         vma = vma_merge(mm, prev, addr, addr + len, flags,
> -                       NULL, NULL, pgoff, NULL, NULL_VM_UFFD_CTX);
> +                       NULL, NULL, pgoff, NULL, NULL_VM_UFFD_CTX, NULL);
>         if (vma)
>                 goto out;
>
> @@ -3250,7 +3256,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
>                 return NULL;    /* should never get here */
>         new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
>                             vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
> -                           vma->vm_userfaultfd_ctx);
> +                           vma->vm_userfaultfd_ctx, vma_anon_name(vma));
>         if (new_vma) {
>                 /*
>                  * Source vma may have been merged into new_vma
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 883e2cc85cad..a48ff8e79f48 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -464,7 +464,7 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
>         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
>         *pprev = vma_merge(mm, *pprev, start, end, newflags,
>                            vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
> -                          vma->vm_userfaultfd_ctx);
> +                          vma->vm_userfaultfd_ctx, vma_anon_name(vma));
>         if (*pprev) {
>                 vma = *pprev;
>                 VM_WARN_ON((vma->vm_flags ^ newflags) & ~VM_SOFTDIRTY);
> --
> 2.33.0.1079.g6e70778dc9-goog
>