Messages in this thread | | | Subject | Re: KVM guest sometimes failed to boot because of kernel stack overflow if KPTI is enabled on a hisilicon ARM64 platform. | From | Wei Xu <> | Date | Wed, 20 Jun 2018 23:52:18 +0800 |
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Hi Will,
On 2018/6/20 22:42, Will Deacon wrote: > 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?
Thanks for you quick response! It can fix our crash but just another walk-around.
>> 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?
Yes.
> >> [ 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. I did not use addr2line before but with gdb we can get same info as below:
(gdb) list *kpti_install_ng_mappings+0x120/0x214 0xffff000008091d70 is in kpti_install_ng_mappings (/home/joyx/plinth-kernel-v200/arch/arm64/kernel/cpufeature.c:907). 902 return !has_cpuid_feature(entry, scope); 903 } 904 905 static void 906 kpti_install_ng_mappings(const struct arm64_cpu_capabilities *__unused) 907 { 908 typedef void (kpti_remap_fn)(int, int, phys_addr_t); 909 extern kpti_remap_fn idmap_kpti_install_ng_mappings; 910 kpti_remap_fn *remap_fn; 911
> 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?
I will try it now. Thanks!
Best Regards, Wei
> Will > > . >
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