linux-kernel - Re: [PATCH 0/4] kaslr: extend movable_node to movable

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Date:   Fri, 20 Oct 2017 10:37:52 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Chao Fan <fanc.fnst@...fujitsu.com>,
        <linux-kernel@...r.kernel.org>, <x86@...nel.org>, <hpa@...or.com>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bhe@...hat.com>,
        <keescook@...omium.org>
CC:     <indou.takao@...fujitsu.com>, <caoj.fnst@...fujitsu.com>
Subject: Re: [PATCH 0/4] kaslr: extend movable_node to
 movable_node=nn[KMG]@ss[KMG]

Hi Chao,

Cheer! I have some concerns below.

At 10/19/2017 06:02 PM, Chao Fan wrote:
> Here is a problem:
> Here is a machine with several NUMA nodes and some of them are hot-pluggable.
> It's not good for kernel to be extracted in the memory region of movable node.
> But in current code, I print the address choosen by kaslr and found it may be
> placed in movable node sometimes. To solve this problem, it's better to limit
> the memory region choosen by kaslr to immovable node in kaslr.c. But the memory
> infomation about if it's hot-pluggable is stored in ACPI SRAT table, which is
> parsed after kernel is extracted. So we can't get the detail memory infomation
> before extracting kernel.
>
> So extend the movable_node to movable_node=nn@ss, in which nn means
> the size of memory in *immovable* node, and ss means the start position of
> this memory region. Then limit kaslr choose memory in these regions.

Yes, great. Here we should remember that the situation of
'movable_node=nn@ss' is rare, normal situation is 'movable_node=nn'.

So, we should consider our code tendencies for normal situation. ;-)

>
> There are two policies:
> 1. Specify the memory region in *movable* node to avoid:
>    Then we can use the existing mem_avoid to handle. But if the memory
>    one movable node was separated by memory hole or different movable nodes
>    are discontinuous, we don't know how many regions need to avoid.

It is not a problem.

As you said, we should provide an interface for users later, like that:

# cat /sys/device/system/memory/movable_node
nn@ss


Thanks,
	dou.
>    OTOH, we must avoid all of the movable memory, otherwise, kaslr may
>    choose the wrong place.
> 2. Specify the memory region in "immovable* node to select:
>    Only support 4 regions in this parameter. Then user can use two nodes
>    at least for kaslr to choose, it's enough for the kernel to extract.
>    At the same time, because we need only 4 new mem_vector, the usage
>    of memory here is not too big.
>
> PATCH 1/4 parse the extended movable_node=nn[KMG]@ss[KMG], then
> 	  store the memory regions.
> PATCH 2/4 selects the memory region in immovable node when process
> 	  memmap.
> PATCH 3/4 is the change of document.
> PATCH 4/4 cleans up some little problems.
>
> Chao Fan (4):
>   kaslr: parse the extended movable_node=nn[KMG]@ss[KMG]
>   kaslr: select the memory region in immovable node to process
>   document: change the document for the extended movable_node
>   kaslr: clean up a useless variable and some usless space
>
>  Documentation/admin-guide/kernel-parameters.txt |   9 ++
>  arch/x86/boot/compressed/kaslr.c                | 140 +++++++++++++++++++++---
>  2 files changed, 131 insertions(+), 18 deletions(-)
>