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Date: Thu, 11 Sep 2014 16:01:10 -0400 From: Vivek Goyal <vgoyal@...hat.com> To: Petr Tesarik <ptesarik@...e.cz> Cc: Eric Biederman <ebiederm@...ssion.com>, kexec@...ts.infradead.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] Put each per-cpu kdump ELF notes into a single page On Fri, Sep 05, 2014 at 06:33:14PM +0200, Petr Tesarik wrote: > On architectures that use percpu-vm, the percpu region is not guaranteed > to be contiguous in physical space. Petr, Which are those arches? > However, fs/proc/vmcore.c expects > all ELF notes to be contiguous. If the ELF note happens to occupy > two non-adjacent physical pages, part of the note may be read from an > incorrect memory location by the kdump kernel, resulting in failure to > initialize /proc/vmcore (if the content of the following physical page, > incorrectly interpreted as an ELF note specifies a large number), wrong > register values or other apparent random memory corruption. > > There is currently no mechanism to pass the virtual-to-physical mapping > of the percpu allocation to the kdump kernel. So, instead, I'm changing > the alignment of the ELF note buffer. Since sizeof(note_buf_t) is less > than PAGE_SIZE, aligning the buffer to the nearest higher power of 2 > is enough to make sure that the buffer cannot cross a page boundary, > effectively ensuring that the whole buffer is contiguous in physical > space. > > Signed-off-by: Petr Tesarik <ptesarik@...e.cz> > --- > kernel/kexec.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/kexec.c b/kernel/kexec.c > index 2bee072..cdab59d 100644 > --- a/kernel/kexec.c > +++ b/kernel/kexec.c > @@ -1610,7 +1610,8 @@ 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); > + crash_notes = __alloc_percpu(sizeof(note_buf_t), > + roundup_pow_of_two(sizeof(note_buf_t))); I think some of the changelog should show up here as comment in short form. I don't think it is obvious that why we are using __alloc_percpu() and why aligning to nearst higher power of 2 is needed here. Please also mention here which arches run into issues. Thanks Vivek > if (!crash_notes) { > pr_warn("Kexec: Memory allocation for saving cpu register states failed\n"); > return -ENOMEM; > -- > 1.8.4.5 > > _______________________________________________ > kexec mailing list > kexec@...ts.infradead.org > http://lists.infradead.org/mailman/listinfo/kexec -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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