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

[Dou Liyang <douly.fnst@cn.fujitsu.com>]

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
>>>> hot-plug.
>>>>
>>>> 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. :)
>

Cc YASUAKI ISHIMATSU

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
> these.
>

Thanks,
	dou.

>>
>>>>
>>>> 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.
>>>>
>>>>
>>>> Thanks,
>>>> 	dou.
>>>>
>>>>>>
>>>>>> 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
>>> placed?
>>>
>>> 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.
>>>
>>> Thanks
>>> Baoquan
>>>
>>>>>>>
>>>>>>> Reported-by: Chao Fan <fanc.fnst@cn.fujitsu.com>
>>>>>>> Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
>>>>>>> ---
>>>>>>> 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)
>>>>>>> 				free(tmp_cmdline);
>>>>>>> 				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;
>>>>>>> 		}
>>>>>>> 	}
>>>>>>>
>>>>>>> --
>>>>>>> 2.5.5
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
>>
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