linux-kernel - Re: [PATCH v2 1/4] kaslr: parse the extended movable

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Date:   Mon, 13 Nov 2017 16:10:41 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Chao Fan <fanc.fnst@...fujitsu.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, douly.fnst@...fujitsu.com
Subject: Re: [PATCH v2 1/4] kaslr: parse the extended
 movable_node=nn[KMG]@ss[KMG]

Hi Chao,

Please think more on your patches, better to discuss with your
colleagues and ask them to help review before your post.

On 11/01/17 at 07:32pm, Chao Fan wrote:
> Extend the movable_node to movable_node=nn[KMG]@ss[KMG].

Firstly, apparently we can't make use of movable_node kernel parameter
and extend it to pass in the immovable_nodes. In fact we are passing in
the memory ranges which can be used for kernel data, not sure if
kernelcore= is OK, or we can make a new one.

Think more about this, or consult your colleagues, FJ has many experts
on mem hotplugging. Choose an proper one or create a new one.

> 
> Since 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 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.
> 
> Signed-off-by: Chao Fan <fanc.fnst@...fujitsu.com>
> ---
>  arch/x86/boot/compressed/kaslr.c | 76 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 75 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index 17818ba6906f..0a591c0023f1 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -107,6 +107,15 @@ 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;

I am fine we support 4 immvoable_mem for now. Please discuss with yor
colleagues, make sure if 4 is OK.

> +
>  static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
>  {
>  	/* Item one is entirely before item two. */
> @@ -167,6 +176,38 @@ 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, movable_node=nn[KMG]
> +		 * has the same behaviour as movable_node=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;
> @@ -206,6 +247,36 @@ static void mem_avoid_memmap(char *str)
>  		memmap_too_large = true;
>  }
>  
> +#ifdef CONFIG_MEMORY_HOTPLUG
> +static void mem_mark_immovable(char *str)

I know you try to imitate the function memblock_mark_hotplug(), but do
you really think you are marking the immovable mem regions? In below
code?

Even if use parse_immovable_mem_regions(), please do not use
mem_mark_immovable.

> +{
> +	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 mem_mark_immovable(char *str)
> +{
> +}
> +#endif
> +
>  static int handle_mem_memmap(void)

Please think of a better function name when you add immovable memory
regions parsing in. Clearly it's not a right name now.

>  {
>  	char *args = (char *)get_cmd_line_ptr();
> @@ -214,7 +285,8 @@ 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 +311,8 @@ static int handle_mem_memmap(void)
>  
>  		if (!strcmp(param, "memmap")) {
>  			mem_avoid_memmap(val);
> +		} else if (!strcmp(param, "movable_node")) {
> +			mem_mark_immovable(val);
>  		} else if (!strcmp(param, "mem")) {
>  			char *p = val;
>  
> -- 
> 2.13.6
> 
> 
>