Re: [PATCH] x86/boot/KASLR: Extend movable_node option for KASLR

From: Dou Liyang
Date: Thu Aug 03 2017 - 23:29:06 EST

At 08/04/2017 10:55 AM, Baoquan He wrote:
On 08/04/17 at 10:42am, Dou Liyang wrote:
Hi Baoquan,

At 08/04/2017 10:00 AM, Baoquan He wrote:
On 08/04/17 at 09:37am, Dou Liyang wrote:
Hi Chao,Baoquan

At 08/04/2017 07:49 AM, Baoquan He wrote:
On 08/03/17 at 08:24pm, Chao Fan wrote:
It's almost another "mem=".

No, it is different.

See Documentation/kernel-parameters:

"mem=" will force usage of a specific amount of memory and kernel will
not see the whole system memory.

But "movable_node=" will not do that.

Then why not using 'mem=' directly?

Before answer this question, let's first discuss why the users want to
replace "mem=" with "movable_node" when they hope to support NUMA node

I guess the real reason is that:

When booting up the system, We should have the whole memory not just
the un-hotpluggable memory which restrict by "mem=", eg:

we boot up kernel with 4 node:

node 0 size: 1024 MB immovable
node 1 size: 1024 MB movable
node 2 size: 1024 MB movable
node 3 size: 1024 MB movable

If we use "mem=1024M" in the command line, we just can use 1G memory.
But actually, we should have 4G normally.

So do you have assumption on the order of immovable nodes and movable
nodes? E.g above your example of nodes, immovable nodes have to be the
lowest address. Is this required by the current hot-plug memory code?

Wow! So great, It seems this is required by the hot-plug memory code.

yesterday, I tested the patch in Qemu with 4 node and each time I
used different node as immovable node. But no matter what node I used,
the immovable nodes always had the lowest address.

I am not familiar with memory, I am investigating this and I am going
to apply for a physical machine with movable nodes to check. :)


could you give us some help!

Great, thanks for your effort. I asked because this question confuses me
and I know FJ ever focusd on the memory hot-plug implementation and
continue working on that, it must be easier for you to consult your
co-workers who ever worked on this. For normal kernel, seems it has
to be that normal zone is on immovable node, namely node0. But what if
people modified bootloader to locate kernel onto the last node and
configure efi firmware to make the last node un-hot-plugable? I believe
both of these can be done. Is this allowed? memory hot-plug has a
requirement about the order of immovable node? And how many immovable
nodes can we have? I have an slides FJ published, didn't find info about


Above is also one reason for why not using 'mem=' directly. Following
is other reasons:

1). each kernel option has its own role, we'd better misuse them.
2). movable_node is used as a boot-time switch to make nodes movable
or not, it should consider any situations, such as KASLR.


On Thu, Aug 03, 2017 at 08:17:21PM +0800, Dou Liyang wrote:
movable_node is a boot-time switch to make hot-pluggable memory
NUMA nodes to be movable. This option is based on an assumption
that any node which the kernel resides in is defined as
un-hotpluggable. Linux can allocates memory near the kernel image
to try the best to keep the kernel away from hotpluggable memory
in the same NUMA node. So other nodes can be movable.

But, KASLR doesn't know which node is un-hotpluggable, the all
hotpluggable memory ranges is recorded in ACPI SRAT table, SRAT
is not parsed. So, KASLR may randomize the kernel in a movable
node which will be immovable.

Extend movable_node option to restrict kernel to be randomized in
immovable nodes by adding a parameter. this parameter sets up
the boundaries between the movable nodes and immovable nodes.

And here you mentioned boundaries, means not only one boundary, so how
do you handle the case movable nodes and immovable nodes alternate to be

I mean, are you sure the current hot-plug memory code require immovable
node has to be the first node and there's only one immovable node or
there are several immovable node but they are the first few nodes?

If yes, then this patch looks good to me, I would like to ack it.


Reported-by: Chao Fan <fanc.fnst@xxxxxxxxxxxxxx>
Signed-off-by: Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>
Documentation/admin-guide/kernel-parameters.txt | 11 +++++++++--
arch/x86/boot/compressed/kaslr.c | 19 ++++++++++++++++---
2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index d9c171c..44c7e33 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2305,7 +2305,8 @@
mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
reporting absolute coordinates, such as tablets

- movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
+ movablecore=nn[KMG]
+ [KNL,X86,IA-64,PPC] This parameter
is similar to kernelcore except it specifies the
amount of memory used for migratable allocations.
If both kernelcore and movablecore is specified,
@@ -2315,12 +2316,18 @@
that the amount of memory usable for all allocations
is not too small.

- movable_node [KNL] Boot-time switch to make hotplugable memory
+ movable_node [KNL] Boot-time switch to make hot-pluggable memory
NUMA nodes to be movable. This means that the memory
of such nodes will be usable only for movable
allocations which rules out almost all kernel
allocations. Use with caution!

+ movable_node=nn[KMG]
+ [KNL] Extend movable_node to work well with KASLR. This
+ parameter is the boundaries between the movable nodes
+ and immovable nodes, the memory which exceeds it will
+ be regarded as hot-pluggable.
MTD_Partition= [MTD]
Format: <name>,<region-number>,<size>,<offset>

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 91f27ab..7e2351b 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -89,7 +89,10 @@ struct mem_vector {
static bool memmap_too_large;

-/* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
+ * Store memory limit specified by the following situations:
+ * "mem=nn[KMG]" or "memmap=nn[KMG]" or "movable_node=nn[KMG]"
+ */
unsigned long long mem_limit = ULLONG_MAX;

@@ -212,7 +215,8 @@ static int handle_mem_memmap(void)
char *param, *val;
u64 mem_size;

- if (!strstr(args, "memmap=") && !strstr(args, "mem="))
+ if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
+ !strstr(args, "movable_node="))
return 0;

tmp_cmdline = malloc(len + 1);
@@ -247,7 +251,16 @@ static int handle_mem_memmap(void)
return -EINVAL;
- mem_limit = mem_size;
+ mem_limit = mem_limit > mem_size ? mem_size : mem_limit;
+ } else if (!strcmp(param, "movable_node")) {
+ char *p = val;
+ mem_size = memparse(p, &p);
+ if (mem_size == 0) {
+ free(tmp_cmdline);
+ return -EINVAL;
+ }
+ mem_limit = mem_limit > mem_size ? mem_size : mem_limit;