Date:   Thu, 18 Jan 2018 08:39:06 -0500
From:   Luiz Capitulino <lcapitulino@...hat.com>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     <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>,
        <indou.takao@...fujitsu.com>
Subject: Re: [PATCH v7 0/5] x86/KASLR: Add parameter
 kaslr_mem=nn[KMG]@ss[KMG]

On Thu, 18 Jan 2018 09:11:14 +0800
Chao Fan <fanc.fnst@...fujitsu.com> wrote:

> On Wed, Jan 17, 2018 at 12:32:35PM -0500, Luiz Capitulino wrote:
> >On Wed, 17 Jan 2018 18:53:46 +0800
> >Chao Fan <fanc.fnst@...fujitsu.com> wrote:
> >  
> >> ***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.  
> >
> >I've tested this series with a 4GB KVM guest. With kaslr_mem=1G, I
> >got one 1GB page allocated 100% of the time in 85 boots. Without
> >kaslr_mem=, I got 3 failures in only 10 boots (that is, in 3 boots
> >I had no 1GB page allocated).
> >
> >So, this series solves the 1GB page problem for me.
> >  
> 
> 
> Thanks for Luiz's test.

Btw, my test tested a simple single case, but I think you can add:

Tested-by: Luiz Capitulino <lcapitulino@...hat.com>

> 
> Thanks,
> Chao Fan
> 
> >> 
> >> 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 said he will do some tests for the 1G huge page issue.
> >> 
> >> ***History
> >> 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(-)
> >>   
> >
> >
> >  
> 
> 

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