linux-kernel - Re: [PATCHv3 1/2] mm/memblock: extend the limit inferior of bottom-up after parsing hotplug attr

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

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