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SubjectRe: [PATCH] kdump: force page alignment for per-CPU crash notes.
On Wed, Feb 29, 2012 at 09:21:23AM -0800, Eugene Surovegin wrote:
> Per-CPU allocations are not guaranteed to be physically contiguous.
> However, kdump kernel and user-space code assumes that per-CPU
> memory, used for saving CPU registers on crash, is.
> This can cause corrupted /proc/vmcore in some cases - the main
> symptom being huge ELF note section.
>
> Force page alignment for note_buf_t to ensure that this assumption holds.

Ouch. I'm surprised there is an allocation on crash, perhaps
it could at least be done earlier? And am I right in thinking
that this change increases the likely hood that the allocation
could fail?

>
> Signed-off-by: Eugene Surovegin <surovegin@google.com>
> CC: Eric Biederman <ebiederm@xmission.com>
> CC: Vivek Goyal <vgoyal@redhat.com>
> CC: kexec-list <kexec@lists.infradead.org>
> ---
> kernel/kexec.c | 9 +++++++--
> 1 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index 7b08867..e641b5c 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -1232,8 +1232,13 @@ 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);
> + /* Allocate memory for saving cpu registers.
> + * Force page alignment to avoid crossing physical page boundary -
> + * kexec-tools and kernel /proc/vmcore handler assume these per-CPU
> + * chunks are physically contiguous.
> + */
> + crash_notes = (note_buf_t __percpu *)__alloc_percpu(sizeof(note_buf_t),
> + PAGE_SIZE);
> if (!crash_notes) {
> printk("Kexec: Memory allocation for saving cpu register"
> " states failed\n");
> --
> 1.7.9.1
>
>
> _______________________________________________
> kexec mailing list
> kexec@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
>


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