Re: Intermittent guest kernel crashes with v4.5-rc6.

[Marc Zyngier <marc.zyngier@arm.com>]

On 02/03/16 13:56, Shanker Donthineni wrote:
> 
> For some reason v4.5-rc6 kernel is not stable for guest machines on 
> Qualcomm server platforms.
> We are getting IABT translation faults while booting the guest kernel. 
> The problem disappears with
> the following code snippet (insert "dsb ish" instruction just before 
> switching to EL1 guest). I am
> using v4.5-rc6 kernel for both host and guest machines.
> 
> Please let me know if you have any thoughts or ideas for tracing this 
> problem.
> 
> --- a/arch/arm64/kvm/hyp/entry.S
> +++ b/arch/arm64/kvm/hyp/entry.S
> @@ -88,6 +88,7 @@ ENTRY(__guest_enter)
>          ldp     x0, x1, [sp], #16
> 
>          // Do not touch any register after this!
> +       dsb ish
>          eret
>   ENDPROC(__guest_enter)
> 
> 
> Using below QEMU command for launching guest machine:
> 
> qemu-system-aarch64 -machine type=virt,accel=kvm,gic-version=3  \
> -cpu "host" -smp cpus=1,maxcpus=1 -m 256M -serial stdio \
> -kernel /boot/Image -initrd /boot/rootfs.cpio.gz \
> -append 'earlycon=earlycon=pl011,0x09000000  \
> console=ttyAMA0,115200 root=/dev/ram'
> 
> 
> Guest machine crash log messages:
> 
> [    0.000000] Booting Linux on physical CPU 0x0
> [    0.000000] Boot CPU: AArch64 Processor [510f2811]
> [    0.000000] Bad mode in Synchronous Abort handler detected, code 
> 0x8600000f -- IABT (current EL)
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.5.rc6+
> [    0.000000] task: ffffffc000d52200 ti: ffffffc000d44000 task.ti: 
> ffffffc000d44000
> [    0.000000] PC is at early_init_dt_scan_root+0x28/0x94
> [    0.000000] LR is at of_scan_flat_dt+0x9c/0xd0
> [    0.000000] pc : [<ffffffc000cb32e8>] lr : [<ffffffc000cb3248>] 
> pstate: 800003c5
> [    0.000000] sp : ffffffc000d47e80
> [    0.000000] x29: ffffffc000d47e80 x28: 0000000000000000
> 

If you're getting a prefetch abort, it would be interesting to find out
what instruction is there, whether the page is mapped at stage-2 or not,
what are the stage-2 permissions... Basically, a full description of the
memory state.

Also, does it work if you do a "dsb ishst" instead?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...