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 . 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 > > > > > >
