Re: [PATCH 1/4] kaslr: parse the extended movable_node=nn[KMG]@ss[KMG]

[Chao Fan]

On Fri, Oct 20, 2017 at 11:41:19AM +0800, Dou Liyang wrote:
>
>
>At 10/20/2017 11:22 AM, Chao Fan wrote:
>> On Fri, Oct 20, 2017 at 11:04:42AM +0800, Dou Liyang wrote:
>> > Hi Chao,
>> > 
>> Hi Dou-san,
>> 
>> > At 10/19/2017 06:02 PM, Chao Fan wrote:
>> > > Extend the movable_node to movable_node=nn[KMG]@ss[KMG].
>> > > Since in current code, kaslr may choose the memory region in hot-pluggable
>> > > nodes. So we can specific the region in immovable node. And store the
>> > > regions in immovable_mem.
>> > > 
>> > 
>> > I guess you may mean that:
>> > 
>> > In current Linux with KASLR. Kernel may choose a memory region in
>> > movable node for extracting kernel code, which will make the node
>> > can't be hot-removed.
>> > 
>> > Solve it by only specific the region in immovable node. So create
>> > immovable_mem to store the region of movable node, and only choose
>> > the memory in immovable_mem array.
>> > 
>> 
>> Thanks for the explaination.
>> 
>> > > Multiple regions can be specified, comma delimited.
>> > > Considering the usage of memory, only support for 4 regions.
>> > > 4 regions contains 2 nodes at least, and is enough for kernel to
>> > > extract.
>> > > 
>> > > Signed-off-by: Chao Fan <fanc.fnst@xxxxxxxxxxxxxx>
>> > > ---
>> > >  arch/x86/boot/compressed/kaslr.c | 63 +++++++++++++++++++++++++++++++++++++++-
>> > >  1 file changed, 62 insertions(+), 1 deletion(-)
>> > > 
>> > > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
>> > > index 17818ba6906f..3c1f5204693b 100644
>> > > --- a/arch/x86/boot/compressed/kaslr.c
>> > > +++ b/arch/x86/boot/compressed/kaslr.c
>> > > @@ -107,6 +107,12 @@ 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
>> > > +
>> > > +static struct mem_vector immovable_mem[MAX_IMMOVABLE_MEM];
>> > > +static int num_immovable_region;
>> > > +
>> > >  static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
>> > >  {
>> > >  	/* Item one is entirely before item two. */
>> > > @@ -167,6 +173,28 @@ 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;
>> > > +
>> > > +	if (*p == '@') {
>> > > +		*start = memparse(p + 1, &p);
>> > > +		return 0;
>> > > +	}
>> > > +
>> > 
>> > Here you don't consider that if @ss[KMG] is omitted.
>> 
>> Yes, will add. Many thanks.
>> 
>> > 
>> > > +	return -EINVAL;
>> > > +}
>> > > +
>> > >  static void mem_avoid_memmap(char *str)
>> > >  {
>> > >  	static int i;
>> > > @@ -206,6 +234,36 @@ static void mem_avoid_memmap(char *str)
>> > >  		memmap_too_large = true;
>> > >  }
>> > > 
>> > > +#ifdef CONFIG_MEMORY_HOTPLUG
>> > > +static void mem_mark_immovable(char *str)
>> > > +{
>> > > +	int i = 0;
>> > > +
>> > 
>> > you have use num_immovable_region, 'i' is useless. just remove it.
>> 
>> Using num_immovable_region makes code too long. Using i will be
>> clear and make sure shoter than 80 characters.
>
>Oh, God, that's horrific. Did you find that your code is wrong?
>
>num_immovable_region will be reset each time.

Did you test?

Thanks,
Chao Fan

>
>Thanks,
>	dou.
>
>> 
>> > 
>> > > +	while (str && (i < MAX_IMMOVABLE_MEM)) {
>> > > +		int rc;
>> > > +		unsigned long long start, size;
>> > > +		char *k = strchr(str, ',');
>> > > +
>> > 
>> > Why do you put this definition here? IMO, moving it out is better.
>> > 
>> > > +		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++;
>> > 
>> > Replace it with num_immovable_region
>> 
>> ditto...
>> Why do you care this little variable so much.
>> 
>> > 
>> > > +	}
>> > > +	num_immovable_region = i;
>> > 
>> > Just remove it.
>> 
>> ditto.
>> 
>> > 
>> > > +}
>> > > +#else
>> > > +static inline void mem_mark_immovable(char *str)
>> > > +{
>> > > +}
>> > > +#endif
>> > > +
>> > >  static int handle_mem_memmap(void)
>> > >  {
>> > >  	char *args = (char *)get_cmd_line_ptr();
>> > > @@ -214,7 +272,8 @@ 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);
>> > > @@ -239,6 +298,8 @@ static int handle_mem_memmap(void)
>> > > 
>> > >  		if (!strcmp(param, "memmap")) {
>> > >  			mem_avoid_memmap(val);
>> > > +		} else if (!strcmp(param, "movable_node")) {
>> > > +			mem_mark_immovable(val);
>> > 
>> > AFAIK, handle_mem_memmap() is invoked in mem_avoid_init(), which is used to
>> > avoid mem. But, here the value of immovable node is the memory
>> > you want to mark and use, it is better that we split it out.
>> 
>> There is existing and useful code, so it's better to reuse but not
>> re-write.
>> 
>> > 
>> > BTW, Using movable_node to store the memory of immovable node is
>> > strange and make me confuse. How about adding a new command option.
>> > 
>> 
>> I have added the document, if you think there are problems, please let
>> me know.
>> 
>> Thanks,
>> Chao Fan
>> 
>> > Thanks,
>> > 	dou.
>> > >  		} else if (!strcmp(param, "mem")) {
>> > >  			char *p = val;
>> > > 
>> > > 
>>