[PATCH v4 0/4] aslr: add parameter immovable_mem=nn[KMG]@ss[KMG] to make memory hotplug work well with kaslr

[Chao Fan]

Here is a problem:
Here is a machine with several NUMA nodes and some of them are
hot-pluggable. It's not good for kernel to be extracted in the memory
region of movable node. But in current code, I print the address chosen by
kaslr and found it may be placed in movable node sometimes.
To solve this problem, it's better to limit the memory region chosen by
kaslr to immovable node in kaslr.c. But the memory information about if
it's hot-pluggable is stored in ACPI SRAT table, which is parsed after
kernel is extracted. So we can't get the detail memory information
before extracting kernel.

So add the new parameter immovable_mem=nn@ss, in which nn means
the size of memory in *immovable* node, and ss means the start position of
this memory region. Then limit kaslr choose memory in these regions.

There are two policies:
1. Specify the memory region in *movable* node to avoid:
   Then we can use the existing mem_avoid to handle. But if the memory
   on movable node was separated by memory hole or different movable nodes
   are discontinuous, we don't know how many regions need to avoid.
   OTOH, we must avoid all of the movable memory, otherwise, kaslr may
   choose the wrong place.
2. Specify the memory region in *immovable* node to select:
   Only support 4 regions in this parameter. Then user can use two nodes
   at least for kaslr to choose, it's enough for the kernel to extract.
   At the same time, because we need only 4 new mem_vector, the usage
   of memory here is not too big. So I think this way is better, and this
   patchset is based on this policy.

PATCH 1/4 parse the new parameter immovable_mem=nn[KMG]@ss[KMG], then
          store the memory regions.
PATCH 2/4 select the memory region in immovable node when process
          memmap.
PATCH 3/4 skip mirror feature if movable_node or immovable_mem specified.
PATCH 4/4 add document.

v1->v2:
Follow Dou Liyang's suggestion:
 - Add the parse for movable_node=nn[KMG] without @ss[KMG]
 - Fix the bug for more than one "movable_node=" specified
 - Drop useless variables and use mem_vector region directely
 - Add more comments.

v2->v3:
Follow Baoquan He's suggestion:
 - Change names of several functions.
 - Add a new parameter "immovable_mem" instead of extending mvoable_node
 - Use the clamp to calculate the memory intersecting, which makes
   logical more clear.
 - Disable memory mirror if movable_node specified

v3->v4:
Follow Kees's suggestion:
 - Put the functions variables of immovable_mem to #ifdef
   CONFIG_MEMORY_HOTPLUG and change some code place
 - Change the name of "process_mem_region" to "slots_count"
 - Reanme the new function "process_immovable_mem" to "process_mem_region"
Follow Baoquan's suggestion:
 - Fail KASLR if "movable_node" specified without "immovable_mem"
 - Ajust the code place of handling mem_region directely if no
   immovable_mem specified
Follow Randy's suggestion:
 - Change the mistake and add detailed description for the document.

Chao Fan (4):
  kaslr: add immovable_mem=nn[KMG]@ss[KMG] to specify extracting memory
  kaslr: calculate the memory region in immovable node
  kaslr: disable memory mirror feature when movable_node
  document: change the document for immovable_mem

 Documentation/admin-guide/kernel-parameters.txt |  10 ++
 arch/x86/boot/compressed/kaslr.c                | 184 ++++++++++++++++++++++--
 2 files changed, 180 insertions(+), 14 deletions(-)

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2.14.3