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| H A D | vmalloc.c | diff d76f99548cf0474c3bf75f25fab1778e03ade5f2 Mon Feb 06 02:40:14 CST 2023 Baoquan He <bhe@redhat.com> mm/vmalloc.c: add used_map into vmap_block to track space of vmap_block
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.com
Signed-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>
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