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kexec: align crash_notes allocation to make it be inside one physical page

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People reported that crash_notes in /proc/vmcore were corrupted and this
cause crash kdump failure.  With code debugging and log we got the root
cause.  This is because percpu variable crash_notes are allocated in 2
vmalloc pages.  Currently percpu is based on vmalloc by default.  Vmalloc
can't guarantee 2 continuous vmalloc pages are also on 2 continuous
physical pages.  So when 1st kernel exports the starting address and size
of crash_notes through sysfs like below:

/sys/devices/system/cpu/cpux/crash_notes
/sys/devices/system/cpu/cpux/crash_notes_size

kdump kernel use them to get the content of crash_notes.  However the 2nd
part may not be in the next neighbouring physical page as we expected if
crash_notes are allocated accross 2 vmalloc pages.  That's why
nhdr_ptr->n_namesz or nhdr_ptr->n_descsz could be very huge in
update_note_header_size_elf64() and cause note header merging failure or
some warnings.

In this patch change to call __alloc_percpu() to passed in the align value
by rounding crash_notes_size up to the nearest power of two.  This makes
sure the crash_notes is allocated inside one physical page since
sizeof(note_buf_t) in all ARCHS is smaller than PAGE_SIZE.  Meanwhile add
a BUILD_BUG_ON to break compile if size is bigger than PAGE_SIZE since
crash_notes definitely will be in 2 pages.  That need be avoided, and need
be reported if it's unavoidable.

[akpm@linux-foundation.org: use correct comment layout]
Signed-off-by: Baoquan He <bhe@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Lisa Mitchell <lisa.mitchell@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Baoquan He 2015-09-09 15:39:00 -07:00 committed by Linus Torvalds
parent 04e9949b2d
commit bbb78b8f3f
1 changed files with 22 additions and 1 deletions
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23
kernel/kexec_core.c
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@ -1004,7 +1004,28 @@ void crash_save_cpu(struct pt_regs *regs, int cpu)
static int __init crash_notes_memory_init(void)
{
/* Allocate memory for saving cpu registers. */
crash_notes = alloc_percpu(note_buf_t);
size_t size, align;
/*
* crash_notes could be allocated across 2 vmalloc pages when percpu
* is vmalloc based . vmalloc doesn't guarantee 2 continuous vmalloc
* pages are also on 2 continuous physical pages. In this case the
* 2nd part of crash_notes in 2nd page could be lost since only the
* starting address and size of crash_notes are exported through sysfs.
* Here round up the size of crash_notes to the nearest power of two
* and pass it to __alloc_percpu as align value. This can make sure
* crash_notes is allocated inside one physical page.
*/
size = sizeof(note_buf_t);
align = min(roundup_pow_of_two(sizeof(note_buf_t)), PAGE_SIZE);
/*
* Break compile if size is bigger than PAGE_SIZE since crash_notes
* definitely will be in 2 pages with that.
*/
BUILD_BUG_ON(size > PAGE_SIZE);
crash_notes = __alloc_percpu(size, align);
if (!crash_notes) {
pr_warn("Kexec: Memory allocation for saving cpu register states failed\n");
return -ENOMEM;