Date:   Thu, 7 Dec 2017 12:16:41 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Chao Fan <fanc.fnst@...fujitsu.com>, Baoquan He <bhe@...hat.com>
CC:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>, <hpa@...or.com>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <keescook@...omium.org>,
        <yasu.isimatu@...il.com>, <indou.takao@...fujitsu.com>,
        <caoj.fnst@...fujitsu.com>
Subject: Re: [PATCH v3 1/4] kaslr: add immovable_mem=nn[KMG]@ss[KMG] to
 specify extracting memory

Hi All,

At 12/07/2017 11:56 AM, Chao Fan wrote:
> On Thu, Dec 07, 2017 at 11:09:24AM +0800, Baoquan He wrote:
>> On 12/07/17 at 10:53am, Chao Fan wrote:
>>> On Wed, Dec 06, 2017 at 05:35:57PM +0800, Baoquan He wrote:
>>>> Hi Chao,
>>>>
>>>> Yes, now the code looks much better than the last version.
>>>>
>>>> On 12/05/17 at 04:51pm, Chao Fan wrote:
>>>>> In current code, kaslr may choose the memory region in movable
>>>>> nodes to extract kernel, which will make the nodes can't be hot-removed.
>>>>> To solve it, we can specify the memory region in immovable node.
>>>>> Create immovable_mem to store the regions in immovable_mem, where should
>>>>> be chosen by kaslr.
>>>>>
>>>>> Multiple regions can be specified, comma delimited.
>>>>> Considering the usage of memory, only support for 4 regions.
>>>>> 4 regions contains 2 nodes at least, enough for kernel to extract.
>>>>>
>>>>> Also change the "handle_mem_memmap" to "handle_mem_filter", since
>>>>> it will not only handle memmap parameter now.
>>>>
>>>> One concern is whether it will fail to do KASLR if only specify
>>>
>>> Sorry, I think I have not understood your point.
>>> So if there is something wrong, please let me know.
>>
>> What I meant is whether we need check 'movable_node' and
>> 'immovable_mem=' being specified together. If only specify 'movable_node',
>> we may need to return and do not do kaslr or do not do physical kaslr
>> since kernel could be located on movable mem region.
>
Indeed.

If *immovable_mem* is valid only when Kernel supports both
KASLR and Node hotplug(movable_node). we need check them together:

...
   else if (!strcmp(param, "movable_node")) {
	if (!strcmp(param, "immovable_mem"))
		parse_immovable_mem_regions(val);
	else
		//no KASLR or no node hotplug?

}
...

> I think both are OK and have reasons, and I tend to not return.
> Because if there is a parameter can solve the problem, but not specified.
> It's a problem of user-level.
> How do you think?
> 

Seems we should clarify the scope of 'immovable_mem=' and document it.

Thanks,
	dou

> Thanks,
> Chao Fan
> 
>>
>> Otherwise it will do physical kaslr anyway, memory hotplug will be
>> impacted later.
>>
>>>
>>> I don't think if only specify "movable_node" will fail KASLR.
>>> Since in this patchset(3/4), only disable kernel mirror. KASLR in
>>> current upstream code didn't parse "movable_node".
>>>
>>>> "movable_node". Surely in this case it won't fail system, just hotplug
>>>> memory might be impacted if kernel is located on that, will FJ mind
>>>
>>> Yes, it's the reason why I make this patchset.
>>> In my personal understanding, "movable_node" is a beginning why I make
>>> this patchset, but not the whole reason.
>>> Only "movable_node" specified might cause hotplug memory can't be
>>> removed if kernel is located on that, so we need the help of
>>> "immovable_mem=". "movable_node" help hotplug memory can be removed, and
>>> "immovable_mem=" works for the same target, but just in kaslr.
>>> So up to now, there is not a very tight coupling between "movable_node"
>>> and "immovable_mem=". The independence of "immovable_mem=" is that,
>>> help kaslr selects the right regions, avoid the memory in hotpluggable
>>> NUMA nodes, which causes the memory can't removed. It's a independent
>>> reason why we need a parameter like "immovable_mem=".
>>> So I think we should also handle it if only specify "immovable_mem="
>>> without "movable_node".
>>>
>>> Thanks,
>>> Chao Fan
>>>
>>>> this? And what if only specify 'immovable_mem=' but without 'movable_node'?
>>>>
>>>> Thanks
>>>> Baoquan
>>>>
>>>>>
>>>>> Signed-off-by: Chao Fan <fanc.fnst@...fujitsu.com>
>>>>> ---
>>>>>   arch/x86/boot/compressed/kaslr.c | 80 ++++++++++++++++++++++++++++++++++++++--
>>>>>   1 file changed, 77 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
>>>>> index a63fbc25ce84..0bbbaf5f6370 100644
>>>>> --- a/arch/x86/boot/compressed/kaslr.c
>>>>> +++ b/arch/x86/boot/compressed/kaslr.c
>>>>> @@ -108,6 +108,15 @@ enum mem_avoid_index {
>>>>>   
>>>>>   static struct mem_vector mem_avoid[MEM_AVOID_MAX];
>>>>>   
>>>>> +/* Only supporting at most 4 immovable memory regions with kaslr */
>>>>> +#define MAX_IMMOVABLE_MEM	4
>>>>> +
>>>>> +/* Store the memory regions in immovable node */
>>>>> +static struct mem_vector immovable_mem[MAX_IMMOVABLE_MEM];
>>>>> +
>>>>> +/* The immovable regions user specify, not more than 4 */
>>>>> +static int num_immovable_region;
>>>>> +
>>>>>   static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
>>>>>   {
>>>>>   	/* Item one is entirely before item two. */
>>>>> @@ -168,6 +177,38 @@ parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
>>>>>   	return -EINVAL;
>>>>>   }
>>>>>   
>>>>> +static int parse_immovable_mem(char *p,
>>>>> +			       unsigned long long *start,
>>>>> +			       unsigned long long *size)
>>>>> +{
>>>>> +	char *oldp;
>>>>> +
>>>>> +	if (!p)
>>>>> +		return -EINVAL;
>>>>> +
>>>>> +	oldp = p;
>>>>> +	*size = memparse(p, &p);
>>>>> +	if (p == oldp)
>>>>> +		return -EINVAL;
>>>>> +
>>>>> +	/* We support nn[KMG]@ss[KMG] and nn[KMG]. */
>>>>> +	switch (*p) {
>>>>> +	case '@':
>>>>> +		*start = memparse(p + 1, &p);
>>>>> +		return 0;
>>>>> +	default:
>>>>> +		/*
>>>>> +		 * If w/o offset, only size specified, immovable_mem=nn[KMG]
>>>>> +		 * has the same behaviour as immovable_mem=nn[KMG]@0. It means
>>>>> +		 * the region starts from 0.
>>>>> +		 */
>>>>> +		*start = 0;
>>>>> +		return 0;
>>>>> +	}
>>>>> +
>>>>> +	return -EINVAL;
>>>>> +}
>>>>> +
>>>>>   static void mem_avoid_memmap(char *str)
>>>>>   {
>>>>>   	static int i;
>>>>> @@ -207,7 +248,37 @@ static void mem_avoid_memmap(char *str)
>>>>>   		memmap_too_large = true;
>>>>>   }
>>>>>   
>>>>> -static int handle_mem_memmap(void)
>>>>> +#ifdef CONFIG_MEMORY_HOTPLUG
>>>>> +static void parse_immovable_mem_regions(char *str)
>>>>> +{
>>>>> +	static int i;
>>>>> +
>>>>> +	while (str && (i < MAX_IMMOVABLE_MEM)) {
>>>>> +		int rc;
>>>>> +		unsigned long long start, size;
>>>>> +		char *k = strchr(str, ',');
>>>>> +
>>>>> +		if (k)
>>>>> +			*k++ = 0;
>>>>> +
>>>>> +		rc = parse_immovable_mem(str, &start, &size);
>>>>> +		if (rc < 0)
>>>>> +			break;
>>>>> +		str = k;
>>>>> +
>>>>> +		immovable_mem[i].start = start;
>>>>> +		immovable_mem[i].size = size;
>>>>> +		i++;
>>>>> +	}
>>>>> +	num_immovable_region = i;
>>>>> +}
>>>>> +#else
>>>>> +static inline void parse_immovable_mem_regions(char *str)
>>>>> +{
>>>>> +}
>>>>> +#endif
>>>>> +
>>>>> +static int handle_mem_filter(void)
>>>>>   {
>>>>>   	char *args = (char *)get_cmd_line_ptr();
>>>>>   	size_t len = strlen((char *)args);
>>>>> @@ -215,7 +286,8 @@ 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, "immovable_mem="))
>>>>>   		return 0;
>>>>>   
>>>>>   	tmp_cmdline = malloc(len + 1);
>>>>> @@ -240,6 +312,8 @@ static int handle_mem_memmap(void)
>>>>>   
>>>>>   		if (!strcmp(param, "memmap")) {
>>>>>   			mem_avoid_memmap(val);
>>>>> +		} else if (!strcmp(param, "immovable_mem")) {
>>>>> +			parse_immovable_mem_regions(val);
>>>>>   		} else if (!strcmp(param, "mem")) {
>>>>>   			char *p = val;
>>>>>   
>>>>> @@ -379,7 +453,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
>>>>>   	/* We don't need to set a mapping for setup_data. */
>>>>>   
>>>>>   	/* Mark the memmap regions we need to avoid */
>>>>> -	handle_mem_memmap();
>>>>> +	handle_mem_filter();
>>>>>   
>>>>>   #ifdef CONFIG_X86_VERBOSE_BOOTUP
>>>>>   	/* Make sure video RAM can be used. */
>>>>> -- 
>>>>> 2.14.3
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
> 

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