Messages in this thread | | | From | Ard Biesheuvel <> | Date | Fri, 13 Nov 2020 07:14:54 +0100 | Subject | Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region |
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On Fri, 13 Nov 2020 at 04:16, Anshuman Khandual <anshuman.khandual@arm.com> wrote: > > > > On 11/12/20 2:55 PM, Catalin Marinas wrote: > > Hi Anshuman, > > > > On Wed, Nov 11, 2020 at 09:18:56AM +0530, 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 > >> > >> 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/ > > > > There was a lot of discussion around this patch but I haven't seen any > > new version posted. > > Just posted before some time. > > https://lore.kernel.org/linux-arm-kernel/1605236574-14636-1-git-send-email-anshuman.khandual@arm.com/ >
You failed to cc me on that patch.
The logic looks correct but please fix up the comment block: - PAGE_END is no longer defined in terms of vabits_actual - bits [51..48] are not ignored by the MMU
Actually, I think the entire second paragraph of that comment block can be dropped.
Please also fix up the coding style: - put && at the end of the first line - drop the redundant parens - fix the indentation
> > > >> 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. > > > > If your patch fixes the randomisation issue that Ard addressed, I'm > > happy to replace that with your patch. But please post a new version and > > get some acks in place from the parties involved in the discussion. > > The above patch is not a replacement for Ard's randomization patch here but > rather complements it. Hence both these patches should be considered, which > will make memory hotplug better on the platform.
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