Date:   Mon, 29 Jan 2018 11:05:28 +0800
From:   Chao Fan <fanc.fnst@...fujitsu.com>
To:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>, <hpa@...or.com>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bhe@...hat.com>,
        <keescook@...omium.org>, <yasu.isimatu@...il.com>
CC:     <indou.takao@...fujitsu.com>, <lcapitulino@...hat.com>
Subject: Re: [PATCH v8 0/5] x86/KASLR: Add parameter kaslr_mem=nn[KMG]@ss[KMG]

Hi Kees,

Since no reply for one week, any suggestions for this version?

Thanks,
Chao Fan

On Tue, Jan 23, 2018 at 04:35:41PM +0800, Chao Fan wrote:
>This is v8 resend. There's no code change. Just improve code comments
>and document accordingly. So add Baoquan's Acked-by and Luiz's
>Tested-by.
>
>***Background:
>People reported that kaslr may randomly chooses some positions
>which are located in movable memory regions. This will break memory
>hotplug feature.
>
>And also on kvm guest with 4GB meory, the good unfragmented 1GB could
>be occupied by randomized kernel. It will cause hugetlb failing to
>allocate 1GB page. While kernel with 'nokaslr' has not such issue.
>This causes regression. Please see the discussion mail:
>        https://lkml.org/lkml/2018/1/4/236
>
>***Solutions:
>Introduce a new kernel parameter 'kaslr_mem=nn@ss' to let users to
>specify the memory regions where kernel can be allowed to randomize
>safely.
>
>E.g if 'movable_node' is spedified, we can use 'kaslr_mem=nn@ss' to
>tell KASLR where we can put kernel safely. Then KASLR code can avoid
>those movable regions and only choose those immovable regions
>specified.
>
>For hugetlb case, users can always add 'kaslr_mem=1G' in kernel
>cmdline since the 0~1G is always fragmented region because of BIOS
>reserved area. Surely users can specify regions more precisely if
>they know system memory very well.
>
>*** Issues need be discussed
>There are several issues I am not quite sure, please help review and
>give suggestions:
>
>1) Since there's already mem_avoid[] which stores the memory regions
>KASLR need avoid. For the regions KASLR can safely use, I name it as
>mem_usable[], not sure if it's appropriate. Or kaslr_mem[] directly?
>
>2) In v6, I made 'kaslr_mem=' as a kernel parameter which users can use
>to specify memory regions where kenrel can be extracted safely by
>'kaslr_mem=nn@ss', or regions where we need avoid to extract kernel by
>'kaslr_mem=nn!ss'. While later I rethink about it, seems
>'kaslr_mem=nn@ss' can satisfy the current requirement, there's no need
>to introduce the 'kaslr_mem=nn!ss'. So I just take that
>'kaslr_mem=nn!ss' handling patch off, may add it later if anyone think
>it's necessary. Any suggestions?
>        https://www.spinics.net/lists/kernel/msg2698457.html
>
>***Test results:
> - I did some tests for the memory hotplug issues. I specify the memory
>   region in one node, then I found every time the kernel will be
>   extracted to the memory of this node.
> - Luiz tested this series with a 4GB KVM guest. With kaslr_mem=1G,
>   got one 1GB page allocated 100% of the time in 85 boots. Without
>   kaslr_mem=, got 3 failures in only 10 boots (that is, in 3 boots
>   no 1GB page allocated). So this series solves the 1GB page problem.
>
>***History
>v7->v8:
> - Just improve some comments.
> - Change the wrong spelling.
> - Add the Tested-by and Acked-by.
>
>v6->v7:
> - Drop the unnecessary avoid part for now.
> - Add document for the new parameter.
>
>v5->v6:
> - Add the last patch to save the avoid memory regions.
>
>v4->v5:
> - Change the problem reported by LKP
>Follow Dou's suggestion:
> - Also return if match "movable_node" when parsing kernel commandline
>   in handle_mem_filter without define CONFIG_MEMORY_HOTPLUG
>
>v3->v4:
>Follow Kees's suggestion:
> - Put the functions variables of immovable_mem to #ifdef
>   CONFIG_MEMORY_HOTPLUG and change some code place
> - Change the name of "process_mem_region" to "slots_count"
> - Reanme the new function "process_immovable_mem" to "process_mem_region"
>Follow Baoquan's suggestion:
> - Fail KASLR if "movable_node" specified without "immovable_mem"
> - Ajust the code place of handling mem_region directely if no
>   immovable_mem specified
>Follow Randy's suggestion:
> - Change the mistake and add detailed description for the document.
>
>v2->v3:
>Follow Baoquan He's suggestion:
> - Change names of several functions.
> - Add a new parameter "immovable_mem" instead of extending mvoable_node
> - Use the clamp to calculate the memory intersecting, which makes
>   logical more clear.
> - Disable memory mirror if movable_node specified
>
>v1->v2:
>Follow Dou Liyang's suggestion:
> - Add the parse for movable_node=nn[KMG] without @ss[KMG]
> - Fix the bug for more than one "movable_node=" specified
> - Drop useless variables and use mem_vector region directely
> - Add more comments.
>
>
>Chao Fan (5):
>  x86/KASLR: Add kaslr_mem=nn[KMG]@ss[KMG]
>  x86/KASLR: Handle the memory regions specified in kaslr_mem
>  x86/KASLR: Give a warning if movable_node specified without kaslr_mem=
>  x86/KASLR: Skip memory mirror handling if movable_node specified
>  document: add document for kaslr_mem
>
> Documentation/admin-guide/kernel-parameters.txt |  10 ++
> arch/x86/boot/compressed/kaslr.c                | 154 +++++++++++++++++++++---
> 2 files changed, 150 insertions(+), 14 deletions(-)
>
>-- 
>2.14.3
>

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