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

[David Hildenbrand]

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@xxxxxxx/
>
> 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