linux-kernel - Re: /proc/vmcore mmap() failure issue

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Message-ID: <52840666.5070800@zytor.com>
Date:	Wed, 13 Nov 2013 15:08:22 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	Kexec Mailing List <kexec@...ts.infradead.org>,
	Baoquan He <bhe@...hat.com>, WANG Chao <chaowang@...hat.com>,
	Dave Young <dyoung@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: /proc/vmcore mmap() failure issue

On 11/13/2013 03:00 PM, Vivek Goyal wrote:
> I think it should be easy to truncate ELF headers in kexec-tools too when
> we are preparing elf headers. I am not sure if it is right thing to do or
> not. If some entry is showing up in /proc/iomem as RAM, then kexec-tools
> need to believe that it is a possibility that kernel is using that pfn and
> that pfn needs to be dumped out in vmcore. IMHO, kernel should fix this
> issue.

The kernel will never use a fractional page, so that is not an issue.

> Secondly, I am writing in-kernel kexec support too and I prepare ELF
> headers there too. And I am facing the same problem there too. So if
> we truncate partial pages in e820 both kexec-tools and in kernel kexec
> implementation don't have to do anything.

I'm mostly worried about truncation upon truncation causing problems.
As long as the trimming is done once and with proper consideration for
abutting regions, I guess I'm okay with it, although it feels wrong to me.

	-hpa

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