linux-kernel - Re: ce56a86e2a ("x86/mm: Limit mmap() of /dev/mem to valid physical addresses"): kernel BUG at arch/x86/mm/physaddr.c:79!

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Date:   Thu, 26 Oct 2017 21:02:29 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Craig Bergstrom <craigb@...gle.com>
Cc:     Sander Eikelenboom <linux@...elenboom.it>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Fengguang Wu <fengguang.wu@...el.com>, wfg@...ux.intel.com,
        linux-kernel@...r.kernel.org, LKP <lkp@...org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: ce56a86e2a ("x86/mm: Limit mmap() of /dev/mem to valid physical
 addresses"): kernel BUG at arch/x86/mm/physaddr.c:79!


* Craig Bergstrom <craigb@...gle.com> wrote:

> Sander, thanks for the details, they've been very useful.
> 
> I suspect that your host system's mem=2048M parameter is causing the
> problem.  Any chance you can confirm by removing the parameter and
> running the guest code path?
> 
> More specifically, since you're telling the kernel that it's high
> memory address is at 2048M and your device is at 0xfe1fe000 (~4G), the
> new mmap() limits are preventing you from mapping addresses that are
> explicitly disallowed by the parameter.

Well, 'mem=2048M' shouldn't really limit device memory, it's supposed to limit 
(trim) 'RAM' and not much else.

Thanks,

	Ingo