Re: -tip tree resume fail, bisect to 5bd5a45(x86: Add NX protectionfor kernel data)

[matthieu castet]

This is a multi-part message in MIME format.matthieu castet a Ãcrit :
> Lin Ming a Ãcrit :
> > On Tue, 2010-11-30 at 19:27 +0800, Peter Zijlstra wrote:
> > > On Tue, 2010-11-30 at 13:00 +0800, Lin Ming wrote:
> > > > echo 0 > /sys/devices/system/cpu/cpu1/online;
> > > > echo 1 > /sys/devices/system/cpu/cpu1/online;
> > > >
> > > > then machine just reboots...
> I tried to do the same thing on qemu, and the same behavior happened (ie 
> reboot when resuming cpu1).
>
> After enabling qemu log, I found that a triple fault was happening at 
> the beginning of secondary_startup_64
> when doing "addq phys_base(%rip), %rax".
>
> Why ?
> I suppose because we access data set to NX, but we don't have enabled 
> yet NX in the msr. So the cpu crash due to "reserved bit check".
>
> If we enable NX before reading data, there is no more crash (patch 
> attached).
>
> Now I am not sure this is the correct fix. I think the problem is that 
> trampoline using kernel page table
> is very dangerous. The kernel can have modified them atfer booting !
> May be all the paging stuff should have been done in head_64.S. A first 
> one with identity mapping, and the second one for
> the real kernel stuff.
Lin, could you try this patch on your x64 machine.


Thanks

Matthieu