linux-kernel - Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

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Date:   Wed, 11 Nov 2020 10:11:03 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Ard Biesheuvel <ardb@...nel.org>
Cc:     Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Steve Capper <steve.capper@....com>,
        Mark Brown <broonie@...nel.org>, Marc Zyngier <maz@...nel.org>,
        gshan@...hat.com, Robin Murphy <robin.murphy@....com>,
        Steven Price <steven.price@....com>
Subject: Re: [PATCH] arm64: mm: account for hotplug memory when randomizing
 the linear region

On 11.11.20 04:48, Anshuman Khandual wrote:
> 
> 
> On 11/11/20 12:44 AM, Catalin Marinas wrote:
>> On Wed, 14 Oct 2020 10:18:57 +0200, Ard Biesheuvel wrote:
>>> As a hardening measure, we currently randomize the placement of
>>> physical memory inside the linear region when KASLR is in effect.
>>> Since the random offset at which to place the available physical
>>> memory inside the linear region is chosen early at boot, it is
>>> based on the memblock description of memory, which does not cover
>>> hotplug memory. The consequence of this is that the randomization
>>> offset may be chosen such that any hotplugged memory located above
>>> memblock_end_of_DRAM() that appears later is pushed off the end of
>>> the linear region, where it cannot be accessed.
>>>
>>> [...]
>>
>> Applied to arm64 (for-next/mem-hotplug), thanks!
>>
>> [1/1] arm64: mm: account for hotplug memory when randomizing the linear region
>>        https://git.kernel.org/arm64/c/97d6786e0669
>>
> 
> Hello Catalin,
> 
> Got delayed and never made here in time, sorry about that. Nonetheless,
> I have got something working with respect to the generic mechanism that
> David Hildenbrand had asked for earlier.
> 
> https://patchwork.kernel.org/project/linux-arm-kernel/patch/1600332402-30123-1-git-send-email-anshuman.khandual@arm.com/
> 
> I am wondering if we could instead consider merging the above patch with
> a small change that Ard had pointed out earlier [1], I will send out a
> revision if required.
> 
> I am asking this because the patch in question is a memory hotplug fix
> and should be back ported to other stable releases. Implementing that
> via the new proposed generic framework might make it difficult for a
> possible arm64 specific backport. We could then add the new generic
> framework and move this fix to an arch callback. Let me know if this
> would be an feasible option. Thank you.

Sure, if it's a fix that is intended to be backported as well, then 
let's move forward with the simple fix and do a proper cleanup on top 
later. Thanks!


-- 
Thanks,

David / dhildenb