From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from tx2ehsobe002.messaging.microsoft.com ([65.55.88.12] helo=tx2outboundpool.messaging.microsoft.com) by merlin.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1UxtMZ-00040P-8a for kexec@lists.infradead.org; Sat, 13 Jul 2013 06:31:25 +0000 Message-ID: <51E0F41A.20904@mail.usask.ca> Date: Sat, 13 Jul 2013 00:30:50 -0600 From: Chris Friesen MIME-Version: 1.0 Subject: Re: visible memory seems wrong in kexec crash dump kernel References: <51DF1BBB.5060904@mail.usask.ca> <51DF2229.5010604@mail.usask.ca> <20130712012142.GA24112@concordia> <51E07056.8040007@mail.usask.ca> <51E08A40.80900@mail.usask.ca> In-Reply-To: <51E08A40.80900@mail.usask.ca> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "kexec" Errors-To: kexec-bounces+dwmw2=twosheds.infradead.org@lists.infradead.org To: Michael Ellerman Cc: Benjamin Herrenschmidt , kexec@lists.infradead.org, Haren Myneni , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, Vivek Goyal On 07/12/2013 04:59 PM, Chris Friesen wrote: > On 07/12/2013 03:08 PM, Chris Friesen wrote: > >> I turned on the instrumentation in early_init_dt_scan_memory() and got >> the following when jumping to the capture kernel: >> >> memory scan node memory, reg size 16, data: 0 0 2 0, >> - 0 , 200000000 >> >> That 0x200000000 matches the fact that I'm seeing 8GB of memory >> available in the recovery kernel. >> >> If I boot the original kernel with "crashkernel=224M@32M", should I >> expect that only 224MB is marked as "linux,usable-memory" in the >> recovery kernel? > > I started looking at the kexec side of things, and I noticed something a > bit odd. In most places dealing with the device tree in kexec it accepts > either "memory" or "memory@" for the memory node name. In > add_usable_mem_property() in arch/ppc64/fs2dt.c it seems to only accept > "memory@". > > Is this expected behaviour? It seems to be the same in current git > versions of kexec-tools. > > On my system I see "/proc/device-tree/memory". > > If I modify add_usable_mem_property() to also accept "/memory" then my > recovery kernel boots up with > > physicalMemorySize = 0x10000000 > > which is 256MB (which is still a bit odd since I specified 224MB for the > crashkernel). > > However, it then hits the BUG() call at the end of mark_bootmem() in > mm/bootmem.c. One final thing and I'll stop replying to myself. :) It looks like the problem is that some board-specific freescale code was calling lmb_reserve() with a base address in the 4GB range. It seems odd that lmb_reserve() didn't throw some kind of error when the recovery kernel was supposed to be limited to 224MB. Rather than try and fix the bug, I turned off the (unneeded) config options related to the above lmb_reserve() calls and was able to successfully access the information I needed via /dev/oldmem. The upshot is that there seems to be a number of things that could be improved: 1) kexec should accept "/memory" and not just "/memory@" 2) lmb_reserve() should really respect the crashkernel memory limit 3) the freescale stuff really shouldn't assume it can map things wherever it feels like Chris _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec