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

From: David Hildenbrand <david@redhat.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	Ard Biesheuvel <ardb@kernel.org>
Cc: Will Deacon <will@kernel.org>,
	linux-kernel@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
	Steve Capper <steve.capper@arm.com>,
	Mark Brown <broonie@kernel.org>, Marc Zyngier <maz@kernel.org>,
	gshan@redhat.com, Robin Murphy <robin.murphy@arm.com>,
	Steven Price <steven.price@arm.com>
Subject: Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region
Date: Wed, 11 Nov 2020 10:11:03 +0100	[thread overview]
Message-ID: <39a6c4a9-bdad-c565-03a0-b60b9811d234@redhat.com> (raw)
In-Reply-To: <a330440d-803b-5aa2-0092-a18317819850@arm.com>

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