From bbb78b8f3f4ea8eca14937b693bfe244838e1d4d Mon Sep 17 00:00:00 2001 From: Baoquan He Date: Wed, 9 Sep 2015 15:39:00 -0700 Subject: [PATCH] kexec: align crash_notes allocation to make it be inside one physical page 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 Cc: Eric W. Biederman Cc: Vivek Goyal Cc: Dave Young Cc: Lisa Mitchell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/kexec_core.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index 9ffc96b65d9a..322dd5579f59 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -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; -- 2.34.1