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Date: Thu, 3 Jan 2019 10:47:06 -0800
From: Tejun Heo <tj@kernel.org>
Subject: Re: [PATCHv3 1/2] mm/memblock: extend the limit inferior of
 bottom-up after parsing hotplug attr
Message-ID: <20190103184706.GU2509588@devbig004.ftw2.facebook.com>
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To: Mike Rapoport <rppt@linux.ibm.com>
Cc: Baoquan He <bhe@redhat.com>, Pingfan Liu <kernelfans@gmail.com>, linux-acpi@vger.kernel.org, linux-mm@kvack.org, kexec@lists.infradead.org, Tang Chen <tangchen@cn.fujitsu.com>, "Rafael J. Wysocki" <rjw@rjwysocki.net>, Len Brown <lenb@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Mike Rapoport <rppt@linux.vnet.ibm.com>, Michal Hocko <mhocko@suse.com>, Jonathan Corbet <corbet@lwn.net>, Yaowei Bai <baiyaowei@cmss.chinamobile.com>, Pavel Tatashin <pasha.tatashin@oracle.com>, Nicholas Piggin <npiggin@gmail.com>, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, Daniel Vacek <neelx@redhat.com>, Mathieu Malaterre <malat@debian.org>, Stefan Agner <stefan@agner.ch>, Dave Young <dyoung@redhat.com>, yinghai@kernel.org, vgoyal@redhat.com, linux-kernel@vger.kernel.org

Hello,

On Wed, Jan 02, 2019 at 07:05:38PM +0200, Mike Rapoport wrote:
> I agree that currently the bottom-up allocation after the kernel text has
> issues with KASLR. But this issues are not necessarily related to the
> memory hotplug. Even with a single memory node, a bottom-up allocation will
> fail if KASLR would put the kernel near the end of node0.
> 
> What I am trying to understand is whether there is a fundamental reason to
> prevent allocations from [0, kernel_start)?
> 
> Maybe Tejun can recall why he suggested to start bottom-up allocations from
> kernel_end.

That's from 79442ed189ac ("mm/memblock.c: introduce bottom-up
allocation mode").  I wasn't involved in that patch, so no idea why
the restrictions were added, but FWIW it doesn't seem necessary to me.

Thanks.

-- 
tejun