On Mon, Mar 19, 2018 at 03:24:46PM +0800, Baoquan He wrote: >On 03/12/18 at 08:04pm, Chao Fan wrote: >> On Mon, Mar 12, 2018 at 11:57:27AM +0100, Ingo Molnar wrote: >> > >> >* Baoquan He <b...@redhat.com> wrote: >> > >> >> Hi Ingo, >> >> >> >> On 03/12/18 at 10:35am, Ingo Molnar wrote: >> >> > >> >> > * Chao Fan <fanc.f...@cn.fujitsu.com> wrote: >> >> > >> >> > > Long time no reply, rebase the patchset, change the parameter name >> >> > > from 'kaslr_mem' to 'kaslr_boot_mem'. There's no more code change. >> >> > > >> >> > > ***Background: >> >> > > People reported that kaslr may randomly chooses some positions >> >> > > which are located in movable memory regions. This will break memory >> >> > > hotplug feature. >> >> > >> >> > [...] >> >> > >> >> > > ***Solutions: >> >> > > Introduce a new kernel parameter 'kaslr_boot_mem=nn@ss' to let users >> >> > > to >> >> > > specify the memory regions where kernel can be allowed to randomize >> >> > > safely. >> >> > >> >> > Manual solutions like that are pretty suboptimal to users, aren't they? >> >> > >> >> > In what way does memory hotplug feature 'break'? Does it crash or >> >> > misbehave? Or >> >> > simply does it not allow the movement of the affected memory region, >> >> > while still >> >> > allowing the rest to be moved? >> >> >> >> AFAIT, if kernel is randomized into the movable memory region, the >> >> affected memory region can not be hot added/removed since it has kernel >> >> data. Surely, the system can still work, the unaffected part still can >> >> be moved. Still it will cause regression on memory hotplug. >> >> >> >> Mainly we parse SRAT table to get the ranges of memory provided by >> >> hot-added memory devices in initmem_init(), that's very late. During boot, >> >> we don't know it. Chao ever posted patches to grab SRAT at decompressing >> >> stage, the code is very complicated and not elegant, ACPI maintainer >> >> NACKed that. > >Hi Chao, > >Seems Ingo prefers the handling in kaslr boot code. Maybe you can try >to optimize and split your below patch and post anouther round? > >I will see how to sove the hugepage in boot/compressed/kaslr.c .
Yes, seems that I need to pick up the old patch and try to optimize it. Thanks, Chao Fan > >Thanks >Baoquan > >> >> Thanks for Ingo's suggestion and Baoquan's explaination. >> >> Yes, I did ever try to dig SRAT table in boot period in early RFC PATCH: >> https://lkml.org/lkml/2017/9/3/77 >> But the change is too huge so made this patchset to avoid this bug in a >> small change, which will not make the code looks messy. >> >> Thanks, >> Chao Fan >> >> > >> >So there's apparently a mis-design here: >> > >> > - KASLR needs to be done very early on during bootup: - it's not realistic >> > to >> > expect KASLR to be done with a booted up kernel, because pointers to >> > various >> > KASLR-ed objects are already widely spread out in memory. >> > >> > - But for some unfathomable reason the memory hotplug attribute of memory >> > regions is not part of the regular memory map but part of late-init ACPI >> > data >> > structures. >> > >> >The right solution would be _not_ to fudge the KASLR location, but to >> >provide the >> >memory hotplug information to early code, preferably via the primary memory >> >map. >> >KASLR can then make use of it and avoid those regions, just like it avoids >> >other >> >memory regions already. >> > >> >In addition to that hardware makers (including virtualized hardware) should >> >also >> >fix their systems to provide memory hotplug information to early code. >> > >> >Thanks, >> > >> > Ingo >> > >> > >> >> > >
