Re: [GIT PULL] x86/kaslr for v3.14

From: H. Peter Anvin
Date: Fri Feb 07 2014 - 11:04:41 EST

On 02/07/2014 06:49 AM, Vivek Goyal wrote:
> Hi Kees,
> Dave Young is testing kdump with kaslr enabled. He is facing some issues.
> One issue he mentioned is that when second kernel boots, it might be
> placed in an area which is outside the reserved area for second kernel.
> We reserve a certain memory for second kernel. And modify memory map of
> second kernel using memmap=exactmap parameter. Looks like kernel placement
> is happening before memmap=exactmap takes effect. And that seems to be
> the reason that second kernel can be placed outside the reserved memory.
> IOW, memmap=exactmap and kaslr don't work together. Is it possible to
> first let memmap=exactmap take affect and then kaslr does its job. Or it
> is too late by the time memmap=exactmap is parsed.
> As a workaround, Dave is currently using "nokaslr" command line parameter
> for second kernel. He is still facing issues where makedumpfile segment
> faults. He is looking into it further.
> I thought I will atleast bring up with issue of memmap=exactmap and kaslr
> being incompatible.

Yes, because memmap=exactmap gets parsed too late; kaslr assumes that
the e820 information passed to it is actually correct.

Yet another cause of breakage caused by the decision on the part of
kdump to rely on command-line options.


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