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

[YASUAKI ISHIMATSU]

On 08/09/2017 10:44 AM, Dou Liyang wrote:
> 
> Hi YASUAKI,
> 
> [...]
>>>>>>>
>>>>>>> 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.
>>
>> I read your patch. And I think what Baoquan wrote is right. The patch does
>> care of only your server. As he wrote, if a server wants to build immovable
>> node onto last node, the patch cannot handle such configuration.
>>
> 
> Thanks for your reviewing. it is reasonable. I will keep in my mind.
> 
> But, I am not sure that  when we boot up a system with the following 4
> nodes, does the BOIS(ACPI firmware) map the immovable node RAM from the
> lowest address first?
> 
> node 0 size: 1024 MB  immovable
> node 1 size: 1024 MB  movable
> node 2 size: 1024 MB  movable
> node 3 size: 1024 MB  immovable
> 
> the order of the physical RAM maps may be node 0, 3, 1, 2.


It depends on SRAT table. If system boots up with movable_node, kernel checks
hot pluggable bit of memory affinity structure in SRAT table. And if hot pluggable
bit is set, the memory will be movable. If not set, the memory will be immovable.

If memory affinity structures in SRAT table are defined as follows, the system
sets up the configuration you mentioned.

PXM: start       : end         : hot pluggable bit
  0:0x00000000000:0x0ffffffffff: disable
  1:0x10000000000:0x1ffffffffff: enable
  2:0x30000000000:0x2ffffffffff: enable
  3:0x40000000000:0x3ffffffffff: disable

We are not sure there is such server. But there is no specification that immovable
node has to be set from lowest address. So kernel should care of such SRAT table.

Thanks,
Yasuaki Ishimatsuu

> 
> 
> Thanks,
> 
>     dou,
> 
>> Thanks,
>> Yasuaki Ishimatsu
>>
>>>>
>>>
>>> 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@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)
>>>>>>>>>>                 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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> 
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