From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from terminus.zytor.com ([2001:1868:205::10] helo=mail.zytor.com) by merlin.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1UQJ5d-0003iC-P0 for kexec@lists.infradead.org; Thu, 11 Apr 2013 15:07:06 +0000 Message-ID: <5166D18A.7090800@zytor.com> Date: Thu, 11 Apr 2013 08:06:50 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 Subject: Re: [PATCH 5/5] kexec: X86: Pass memory ranges via e820 table instead of memmap= boot parameter References: <1365683207-42425-1-git-send-email-trenn@suse.de> <1365683207-42425-6-git-send-email-trenn@suse.de> In-Reply-To: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=twosheds.infradead.org@lists.infradead.org To: Yinghai Lu Cc: "kexec@lists.infradead.org" , Linux Kernel Mailing List , Thomas Renninger , Simon Horman , "Eric W. Biederman" , Cliff Wickman , Vivek Goyal On 04/11/2013 07:55 AM, Yinghai Lu wrote: > On Thu, Apr 11, 2013 at 5:26 AM, Thomas Renninger wrote: >> Currently ranges are passed via kernel boot parameters: >> memmap=exactmap memmap=X#Y memmap= >> >> Pass them via e820 table directly instead. > > how to address "saved_max_pfn" referring in kernel? > > kernel need to use saved_max_pfn from old e820 in > drivers/char/mem.c::read_oldmem() > > mips and powerpc they are passing that from command line "savemaxmem=" > > x86 should use that too? > Oh bloody hell, yet another f-ing "max_pfn" variable. The *only* one that makes any kind of sense is max_low_pfn (marking the cutoff to highmem)... the pretty much the rest of them are just plain wrong. And I don't mean "mildly annoying", I mean "catastrophically wrong semantics". In this case, it introduces a completely arbitrary distinction between a nonmemory range below a high water mark and a nonmemory range above that high water mark. In fact, from reading the code it seems pretty clear that the device will blindly assume that anything below saved_max_pfn is memory and will try to map it cachable... which will #MC on quite a few machines. This kind of crap HAS TO STOP. Memory is discontiguous, deal with it and deal with it properly. I also have to admit that I don't see the difference between /dev/mem and /dev/oldmem, as the former allows access to memory ranges outside the ones used by the current kernel, which is what the oldmem device seems to be intended to od. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec