ANDROID: mm: add a field to store names for private anonymous memory

Userspace processes often have multiple allocators that each do
anonymous mmaps to get memory.  When examining memory usage of
individual processes or systems as a whole, it is useful to be
able to break down the various heaps that were allocated by
each layer and examine their size, RSS, and physical memory
usage.

This patch adds a user pointer to the shared union in
vm_area_struct that points to a null terminated string inside
the user process containing a name for the vma.  vmas that
point to the same address will be merged, but vmas that
point to equivalent strings at different addresses will
not be merged.

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 names of named anonymous vmas are shown in /proc/pid/maps
as [anon:<name>] and in /proc/pid/smaps in a new "Name" field
that is only present for named vmas.  If the userspace pointer
is no longer valid all or part of the name will be replaced
with "<fault>".

The idea to store a userspace pointer to reduce the complexity
within mm (at the expense of the complexity of reading
/proc/pid/mem) came from Dave Hansen.  This results in no
runtime overhead in the mm subsystem other than comparing
the anon_name pointers when considering vma merging.  The pointer
is stored in a union with fieds that are only used on file-backed
mappings, so it does not increase memory usage.

Includes fix from Jed Davis <jld@mozilla.com> for typo in
prctl_set_vma_anon_name, which could attempt to set the name
across two vmas at the same time due to a typo, which might
corrupt the vma list.  Fix it to use tmp instead of end to limit
the name setting to a single vma at a time.

Bug: 120441514
Change-Id: I9aa7b6b5ef536cd780599ba4e2fba8ceebe8b59f
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>
[AmitP: Fix get_user_pages_remote() call to align with upstream commit
        5b56d49fc31d ("mm: add locked parameter to get_user_pages_remote()")]
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
[ebiggers: folded in fixes from the following commits:
           1da58ab55546 ("ANDROID: fix up direct access to mmap_sem")
           7df9282d8ecb ("ANDROID: mm: fix up new call to vma_merge()")]
           b5c8a97d5085 ("ANDROID: fix up 60500a42286d ("ANDROID: mm:
                          add a field to store names for private
                          anonymous memory")")
Signed-off-by: Eric Biggers <ebiggers@google.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 533c79e8d2cd..e72c93161134 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -429,6 +429,8 @@ 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.
@@ -462,6 +464,7 @@ Memory Area, or VMA) there is a series of lines such as the following::
     Locked:                0 kB
     THPeligible:           0
     VmFlags: rd ex mr mw me dw
+    Name: name from userspace
 
 The first of these lines shows the same information as is displayed for the
 mapping in /proc/PID/maps.  Following lines show the size of the mapping
@@ -554,6 +557,9 @@ be vanished or the reverse -- new added. Interpretation of their meaning
 might change in future as well. So each consumer of these flags has to
 follow each specific kernel version for the exact semantic.
 
+The "Name" field will only be present on a mapping that has been named by
+userspace, and will show the name passed in by userspace.
+
 This file is only present if the CONFIG_MMU kernel configuration option is
 enabled.