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* [PATCH v2 0/7] mm/vmalloc.c: allow vread() to read out vm_map_ram areas
@ 2022-12-17  1:54 Baoquan He
  2022-12-17  1:54 ` [PATCH v2 1/7] mm/vmalloc.c: add used_map into vmap_block to track space of vmap_block Baoquan He
                   ` (6 more replies)
  0 siblings, 7 replies; 32+ messages in thread
From: Baoquan He @ 2022-12-17  1:54 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-mm, urezki, stephen.s.brennan, willy, akpm, hch, Baoquan He

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 about
it:

  /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 passed out. However, area reserved through vm_map_ram() interface
doesn't allocate vm_struct to bind with. So the current code in vread()
will skip the vm_map_ram area through 'if (!va->vm)' conditional checking.

Solution:
***
There are two types of vm_map_ram area. One is the whole vmap_area being
reserved and mapped at one time; the other is the whole vmap_area with
VMAP_BLOCK_SIZE size being reserved at one time, while mapped into split
regions with smaller size several times via vb_alloc(). I will call the
2nd type vb region.

In patch 1 and 2, add flags into struct vmap_area to mark these two types
of vm_map_ram area, meanwhile add bitmap field used_map into struct
vmap_block to mark those vb 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 them in vread() and handle them respectively in patch 3.

Besides,
***
In patch 5, let's ignore vmap area with VM_UNINITIALIZED set in
vm->flags, because this kind of area is created by calling
__vmalloc_node_range(), VM_UNINITIALIZED set indicating it has
vm_struct associated with, but is still during the page allocating and
mapping process.

In patch 6 and 7, change area flag from VM_ALLOC to VM_IOREMAP in two
places. This will show them as 'ioremap' in /proc/vmallocinfo, and
exclude them from /proc/kcore.

Testing
***
Only did the basic testing.

Changelog
***
v1->v2:
- Change alloc_vmap_area() to pass in va_flags so that we can pass and
  set vmap_area->flags for vm_map_ram area. With this, no extra action
  need be added to acquire vmap_area_lock when doing the vmap_area->flags
  setting. Uladzislau reviewed v1 and pointed out the issue.
- Improve vb_vread() to cover the case where reading is started from a
  dirty or free region.

RFC->v1:
- Add a new field flags in vmap_area to mark vm_map_ram area. It cold be
  risky reusing the vm union in vmap_area in RFC. I will consider
  reusing the union in vmap_area to save memory later. Now just take the
  simpler way to let's focus on resolving the main problem.
- Add patch 4~7 for optimization.

Baoquan He (7):
  mm/vmalloc.c: add used_map into vmap_block to track space of
    vmap_block
  mm/vmalloc.c: add flags to mark vm_map_ram area
  mm/vmalloc.c: allow vread() to read out vm_map_ram areas
  mm/vmalloc: explicitly identify vm_map_ram area when shown in
    /proc/vmcoreinfo
  mm/vmalloc: skip the uninitilized vmalloc areas
  powerpc: mm: add VM_IOREMAP flag to the vmalloc area
  sh: mm: set VM_IOREMAP flag to the vmalloc area

 arch/powerpc/kernel/pci_64.c |   2 +-
 arch/sh/kernel/cpu/sh4/sq.c  |   2 +-
 include/linux/vmalloc.h      |   1 +
 mm/vmalloc.c                 | 106 +++++++++++++++++++++++++++++------
 4 files changed, 92 insertions(+), 19 deletions(-)

-- 
2.34.1


^ permalink raw reply	[flat|nested] 32+ messages in thread

end of thread, other threads:[~2023-01-18 13:00 UTC | newest]

Thread overview: 32+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-12-17  1:54 [PATCH v2 0/7] mm/vmalloc.c: allow vread() to read out vm_map_ram areas Baoquan He
2022-12-17  1:54 ` [PATCH v2 1/7] mm/vmalloc.c: add used_map into vmap_block to track space of vmap_block Baoquan He
2022-12-17  1:54 ` [PATCH v2 2/7] mm/vmalloc.c: add flags to mark vm_map_ram area Baoquan He
2022-12-17 11:44   ` Lorenzo Stoakes
2022-12-19  8:01     ` Baoquan He
2022-12-19  9:09       ` Lorenzo Stoakes
2022-12-19 12:24         ` Baoquan He
2022-12-19 13:01           ` Lorenzo Stoakes
2022-12-20 12:14             ` Baoquan He
2022-12-20 12:42               ` Lorenzo Stoakes
2022-12-20 16:55   ` Uladzislau Rezki
2022-12-23  4:14     ` Baoquan He
2023-01-13  3:55       ` Baoquan He
2023-01-16 17:54         ` Uladzislau Rezki
2023-01-18  3:09           ` Baoquan He
2023-01-18 12:20             ` Uladzislau Rezki
2022-12-17  1:54 ` [PATCH v2 3/7] mm/vmalloc.c: allow vread() to read out vm_map_ram areas Baoquan He
2022-12-17  4:10   ` kernel test robot
2022-12-17  6:41   ` kernel test robot
2022-12-17  9:46     ` Baoquan He
2022-12-17 12:06   ` Lorenzo Stoakes
2023-01-04  8:01     ` Baoquan He
2023-01-04 20:20       ` Lorenzo Stoakes
2023-01-09  4:35         ` Baoquan He
2023-01-09  7:12           ` Lorenzo Stoakes
2023-01-09 12:49             ` Baoquan He
2022-12-17  1:54 ` [PATCH v2 4/7] mm/vmalloc: explicitly identify vm_map_ram area when shown in /proc/vmcoreinfo Baoquan He
2022-12-17  1:54 ` [PATCH v2 5/7] mm/vmalloc: skip the uninitilized vmalloc areas Baoquan He
2022-12-17 12:07   ` Lorenzo Stoakes
2022-12-19  7:16     ` Baoquan He
2022-12-17  1:54 ` [PATCH v2 6/7] powerpc: mm: add VM_IOREMAP flag to the vmalloc area Baoquan He
2022-12-17  1:54 ` [PATCH v2 7/7] sh: mm: set " Baoquan He

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