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

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Message-ID: <2e84fa4b-f35b-5ecf-5b67-f570bdd29a06@arm.com>
Date:   Fri, 13 Nov 2020 13:10:01 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <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>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH] arm64: mm: account for hotplug memory when randomizing
 the linear region



On 11/13/20 12:36 PM, Ard Biesheuvel wrote:
> On Fri, 13 Nov 2020 at 08:03, Anshuman Khandual
> <anshuman.khandual@....com> wrote:
>>
>>
>>
>> On 11/13/20 11:44 AM, Ard Biesheuvel wrote:
>>> On Fri, 13 Nov 2020 at 04:16, Anshuman Khandual
>>> <anshuman.khandual@....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.
>>
>> I could see 'ardb@...nel.org' marked as a copy on the patch. You
>> did not receive the email ? The CC list is in the commit message
>> itself. Even the lore.kernel.org based URL does list you email
>> as well. Not sure what might have happened.
>>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will@...nel.org>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: Ard Biesheuvel <ardb@...nel.org>
>> Cc: Steven Price <steven.price@....com>
>> Cc: Robin Murphy <robin.murphy@....com>
>> Cc: David Hildenbrand <david@...hat.com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Cc: linux-kernel@...r.kernel.org
>>
> 
> Right. Not sure what happened there, I may have deleted it by
> accident. Apologies.
> 
>>>
>>> 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.
>>
>> And from the commit message as well, had reused it in both places.
>>
>>>
>>> Please also fix up the coding style:
>>> - put && at the end of the first line
>>> - drop the redundant parens
>>> - fix the indentation
>>
>> Does this look okay ?
>>
>> static bool inside_linear_region(u64 start, u64 size)
>> {
>>         /*
>>          * Linear mapping region is the range [PAGE_OFFSET..(PAGE_END - 1)]
>>          * accommodating both its ends but excluding PAGE_END. Max physical
>>          * range which can be mapped inside this linear mapping range, must
>>          * also be derived from its end points.
>>          */
>>         return start >= __pa(_PAGE_OFFSET(vabits_actual)) &&
>>                         (start + size - 1) <= __pa(PAGE_END - 1);
>> }
> 
> Not sure whether the whitespace has been mangled by the email client,
> but the first ( on the second line should align vertically with the
> 's' of 'start' on the first line

It was not aligned vertically here but fixed it. I hope you have received
the latest version this time.

https://lore.kernel.org/linux-arm-kernel/1605252614-761-1-git-send-email-anshuman.khandual@arm.com/