Hi Michael! > The Linux kernel for powerpc since v5.2 has a bug which allows a > malicious KVM guest to crash the host, when the host is running on > Power8. > > Only machines using Linux as the hypervisor, aka. KVM, powernv or bare > metal, are affected by the bug. Machines running PowerVM are not > affected. > > The bug was introduced in: > > 10d91611f426 ("powerpc/64s: Reimplement book3s idle code in C") > > Which was first released in v5.2. > > The upstream fix is: > > cdeb5d7d890e ("KVM: PPC: Book3S HV: Make idle_kvm_start_guest() return 0 if > it went to guest") > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cdeb5d7d890e14f3b70e8087e745c4a6a7d9f337 > > Which will be included in the v5.16 release.
I have tested these patches against 5.14 but it seems the problem [1] still remains for me for big-endian guests. I built a patched kernel yesterday, rebooted the KVM server and let the build daemons do their work over night. When I got up this morning, I noticed the machine was down, so I checked the serial console via IPMI and saw the same messages again as reported in [1]: [41483.963562] watchdog: BUG: soft lockup - CPU#104 stuck for 25521s! [migration/104:175] [41507.963307] watchdog: BUG: soft lockup - CPU#104 stuck for 25544s! [migration/104:175] [41518.311200] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [41518.311216] rcu: 136-...0: (135 ticks this GP) idle=242/1/0x4000000000000000 softirq=32031/32033 fqs=2729959 [41547.962882] watchdog: BUG: soft lockup - CPU#104 stuck for 25581s! [migration/104:175] [41571.962627] watchdog: BUG: soft lockup - CPU#104 stuck for 25603s! [migration/104:175] [41581.330530] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [41581.330546] rcu: 136-...0: (135 ticks this GP) idle=242/1/0x4000000000000000 softirq=32031/32033 fqs=2736378 [41611.962202] watchdog: BUG: soft lockup - CPU#104 stuck for 25641s! [migration/104:175] [41635.961947] watchdog: BUG: soft lockup - CPU#104 stuck for 25663s! [migration/104:175] [41644.349859] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [41644.349876] rcu: 136-...0: (135 ticks this GP) idle=242/1/0x4000000000000000 softirq=32031/32033 fqs=2742753 [41671.961564] watchdog: BUG: soft lockup - CPU#104 stuck for 25697s! [migration/104:175] [41695.961309] watchdog: BUG: soft lockup - CPU#104 stuck for 25719s! [migration/104:175] [41707.369190] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [41707.369206] rcu: 136-...0: (135 ticks this GP) idle=242/1/0x4000000000000000 softirq=32031/32033 fqs=2749151 [41735.960884] watchdog: BUG: soft lockup - CPU#104 stuck for 25756s! [migration/104:175] [41759.960629] watchdog: BUG: soft lockup - CPU#104 stuck for 25778s! [migration/104:175] [41770.388520] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [41770.388548] rcu: 136-...0: (135 ticks this GP) idle=242/1/0x4000000000000000 softirq=32031/32033 fqs=2755540 [41776.076307] rcu: rcu_sched kthread timer wakeup didn't happen for 1423 jiffies! g49897 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 [41776.076327] rcu: Possible timer handling issue on cpu=32 timer-softirq=1056014 [41776.076336] rcu: rcu_sched kthread starved for 1424 jiffies! g49897 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=32 [41776.076350] rcu: Unless rcu_sched kthread gets sufficient CPU time, OOM is now expected behavior. [41776.076360] rcu: RCU grace-period kthread stack dump: [41776.076434] rcu: Stack dump where RCU GP kthread last ran: [41783.960374] watchdog: BUG: soft lockup - CPU#104 stuck for 25801s! [migration/104:175] [41807.960119] watchdog: BUG: soft lockup - CPU#104 stuck for 25823s! [migration/104:175] [41831.959864] watchdog: BUG: soft lockup - CPU#104 stuck for 25846s! [migration/104:175] [41833.407851] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [41833.407868] rcu: 136-...0: (135 ticks this GP) idle=242/1/0x4000000000000000 softirq=32031/32033 fqs=2760381 [41863.959524] watchdog: BUG: soft lockup - CPU#104 stuck for 25875s! [migration/104:175] It seems that in this case, it was the testsuite of the git package [2] that triggered the bug. As you can see from the overview, the git package has been in the building state for 8 hours meaning the build server crashed and is no longer giving feedback to the database. Adrian > [1] https://bugzilla.kernel.org/show_bug.cgi?id=206669 > [2] https://buildd.debian.org/status/package.php?p=git&suite=experimental -- .''`. John Paul Adrian Glaubitz : :' : Debian Developer - glaub...@debian.org `. `' Freie Universitaet Berlin - glaub...@physik.fu-berlin.de `- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913