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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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