Patch series "mm/vmalloc.c: allow vread() to read out vm_map_ram areas", v5.

Problem:
***

Stephen reported vread() will skip vm_map_ram areas when reading out
/proc/kcore with drgn utility.  Please see below link to get more details.
 

  /proc/kcore reads 0's for vmap_block
  https://lore.kernel.org/all/87ilk6gos2.fsf@oracle.com/T/#u

Root cause:
***

The normal vmalloc API uses struct vmap_area to manage the virtual kernel
area allocated, and associate a vm_struct to store more information and
pass out.  However, area reserved through vm_map_ram() interface doesn't
allocate vm_struct to associate with.  So the current code in vread() will
skip the vm_map_ram area through 'if (!va->vm)' conditional checking.

Solution:
***

To mark the area reserved through vm_map_ram() interface, add field
'flags' into struct vmap_area.  Bit 0 indicates this is vm_map_ram area
created through vm_map_ram() interface, bit 1 marks out the type of
vm_map_ram area which makes use of vmap_block to manage split regions via
vb_alloc/free().

And also add bitmap field 'used_map' into struct vmap_block to mark those
further subdivided regions being used to differentiate with dirty and free
regions in vmap_block.

With the help of above vmap_area->flags and vmap_block->used_map, we can
recognize and handle vm_map_ram areas successfully.  All these are done in
patch 1~3.

Meanwhile, do some improvement on areas related to vm_map_ram areas in
patch 4, 5.  And also change area flag from VM_ALLOC to VM_IOREMAP in
patch 6, 7 because this will show them as 'ioremap' in /proc/vmallocinfo,
and exclude them from /proc/kcore.


This patch (of 7):

In one vmap_block area, there could be three types of regions: region
being used which is allocated through vb_alloc(), dirty region which is
freed via vb_free() and free region.  Among them, only used region has
available data.  While there's no way to track those used regions
currently.

Here, add bitmap field used_map into vmap_block, and set/clear it during
allocation or freeing regions of vmap_block area.

This is a preparation for later use.

Link: https://lkml.kernel.org/r/20230206084020.174506-1-bhe@redhat.com
Link: https://lkml.kernel.org/r/20230206084020.174506-2-bhe@redhat.comSigned-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Dan Carpenter <error27@gmail.com>
Cc: Stephen Brennan <stephen.s.brennan@oracle.com>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>