Messages in this thread | | | Date | Fri, 20 Oct 2017 11:46:15 +0800 | From | Chao Fan <> | Subject | Re: [PATCH 0/4] kaslr: extend movable_node to movable_node=nn[KMG]@ss[KMG] |
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On Fri, Oct 20, 2017 at 11:37:11AM +0800, Dou Liyang wrote: >Hi Chao, > >At 10/20/2017 10:53 AM, Chao Fan wrote: >> On Fri, Oct 20, 2017 at 10:37:52AM +0800, Dou Liyang wrote: >> > Hi Chao, >> > >> Hi Dou-san, >> >> > Cheer! I have some concerns below. >> >> Thanks for your reply. >> >> > >> > 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. ;-) >> >> Yes, it's normal. But you can not make sure the special situation will >> never happen,. If it happens, we can make sure codes work well, right? >> >> We can not make sure that the movable nodes are continuous, or even if >> the movable nodes are continuous, we can not make sure the memory >> address are continuous. >> >> It is easy to avoid the memory region in movable node. >> But if we can handle more special situations, and at the same time, >> make kernel more safe, why not? > >You misunderstand my opinions, I means that >when we code, we need to know the problem clearly and which part of >problem will often be executed. > >Make our code more suitable for the normal situation without affecting the >function of the problem. >Just like: > >likely() and unlikely() Hi Dou-san,
Thanks for that. I think likely() is suitable for another place.
Thanks, Chao Fan
> >Here I guess you don't consider that. so I said that. > >> >> > >> > > >> > > 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 >> > >> >> Both are OK. I think outputing the memory region in movable_node or >> immovable_node are both reasonable. So the interface of both methods >> will be useful. And after we decided which policy used in kaslr, then >> add the interface of /sys. >> > >Actually, I prefer the first one, are you ready to post the patches >for the first policy? > >Thanks, > dou. >> Thanks, >> Chao Fan >> >> > >> > 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(-) >> > > >>
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