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

Chao Fan
2017-10-20T03:44:53Z

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@cn.fujitsu.com>
>> > > ---
>> > > 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;
>> > >
>> > >
>>