Messages in this thread | | | Date | Wed, 20 Jun 2018 15:42:58 +0100 | From | Will Deacon <> | Subject | Re: KVM guest sometimes failed to boot because of kernel stack overflow if KPTI is enabled on a hisilicon ARM64 platform. |
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Hi Wei,
On Wed, Jun 20, 2018 at 10:18:00PM +0800, Wei Xu wrote: > We have observed KVM guest sometimes failed to boot because of kernel stack > overflow if KPTI is enabled on a hisilicon arm64 platform. > > We also tested with different kernel version and found it is only > happened if the KPTI and KVM(enable-kvm & cpu=host) are enabled on the > guest. > The detail result is as below table. > > +---------+----------+--------+------------+-------------------+ > | host |host KPTI | guest | guest KPTI | kvm guest | > | kernel |enabled | kernel | enabled | booting result | > +---------+----------+--------+------------+-------------------+ > | 4.17 | Y | 4.17 | Y | stack overflow | > +---------+----------+--------+------------+-------------------+ > | 4.17 | Y | 4.16 | NA | OK | > +---------+----------+--------+------------+-------------------+ > | 4.16 | NA | 4.17 | Y | stack overflow | > +---------+----------+--------+------------+-------------------+ > | 4.16 | NA | 4.16 | NA | OK | > +---------+----------+--------+------------+-------------------+ > > A simple walk-around is adding this platform into the "kpti_safe_list". > But it does not resolve the issue indeed. > Could you please share any hint how to resolve this kind issue? > Thanks! > > Another issue we found is "kpti_install_ng_mappings" will be invoked > even "kpti=off" has been added in the kernel command line. Is that expected? > This is because "kpti" is not a *early* param that "init_cpu_features" will > be invoked before parsing the param.
That sounds like a straightforward bug, which means we should use early_param instead of __setup. I assume that doesn't fix your crash, though?
> The command we are using to run the guest is as: > > ./qemu-system-aarch64 -machine virt,kernel_irqchip=on,gic-version=3 -cpu > host > -enable-kvm -smp 1 -m 1024 -kernel ./Image -initrd > ../mini-rootfs-arm64.cpio.gz > -nographic -append "rdinit=init console=ttyAMA0 > earlycon=pl011,0x9000000" > > The log is as below: > > [ 0.000000] Booting Linux on physical CPU 0x0000000000 > [0x480fd010] > [ 0.000000] Linux version 4.17.0-45864-g29dcea8-dirty > (joyx@Turing-Arch-b) (gcc version 4.9.1 20140505 (prerelease) (crosstool-NG > linaro-1.13.1-4.9-2014.05 - Linaro GCC 4.9-2014.05)) #6 SMP PREEMPT Fri Jun > 15 21:39:52 CST 2018
^^^ This is reproducible with vanilla v4.17 and defconfig, right?
> [ 0.038859] SMP: Total of 1 processors activated. > [ 0.039338] CPU features: detected: GIC system register CPU > interface > [ 0.039988] CPU features: detected: Privileged Access Never > [ 0.040560] CPU features: detected: User Access Override > [ 0.041093] CPU features: detected: RAS Extension Support > [ 0.042947] Insufficient stack space to handle exception! > [ 0.042949] ESR: 0x96000046 -- DABT (current EL) > [ 0.043963] FAR: 0xffff0000093a80e0 > [ 0.045794] Task stack: [0xffff0000093a8000..0xffff0000093ac000] > [ 0.052181] IRQ stack: [0xffff000008000000..0xffff000008004000] > [ 0.058572] Overflow stack: > [0xffff80003efce2f0..0xffff80003efcf2f0] > [ 0.065068] CPU: 0 PID: 12 Comm: migration/0 Not tainted > 4.17.0-45864-g29dcea8-dirty #6 > [ 0.073138] Hardware name: linux,dummy-virt (DT) > [ 0.077831] pstate: 604003c5 (nZCv DAIF +PAN -UAO) > [ 0.082661] pc : el1_sync+0x0/0xb0 > [ 0.086152] lr : kpti_install_ng_mappings+0x120/0x214
Can you use scripts/faddr2line to find out which line of code the lr is pointing at, please? It would be interesting to know if we managed to install the idmap.
Hmm, I wonder if this is at all related to RAS, since we've just enabled that and if we take a fault whilst rewriting swapper then we're going to get stuck. What happens if you set CONFIG_ARM64_RAS_EXTN=n in the guest?
Will
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