On 11/26/2015 05:17 PM, Tyler Baker wrote: > Hi Christian, > > The kernelci.org bot recently has been reporting kvm guest boot > failures[1] on various arm64 platforms in next-20151126. The bot > bisected[2] the failures to the commit in -next titled "KVM: Create > debugfs dir and stat files for each VM". I confirmed by reverting this > commit on top of next-20151126 it resolves the boot issue. > > In this test case the host and guest are booted with the same kernel. > The host is booted over nfs, installs qemu (qemu-system arm64 2.4.0), > and launches a guest. The host is booting fine, but when the guest is > launched it errors with "Failed to retrieve host CPU features!". I > checked the host logs, and found an "Unable to handle kernel paging > request" splat[3] which occurs when the guest is attempting to start. > > I scanned the patch in question but nothing obvious jumped out at me, > any thoughts? Not really. Do you have processing running that do read the files in /sys/kernel/debug/kvm/* ? If I read the arm oops message correctly it oopsed inside __srcu_read_lock. there is actually nothing in there that can oops, except the access to the preempt count. I am just guessing right now, but maybe the preempt variable is no longer available (as the process is gone). As long as a debugfs file is open, we hold a reference to the kvm, which holds a reference to the mm, so the mm might be killed after the process. But this is supposed to work, so maybe its something different. An objdump of __srcu_read_lock might help. I will drop it from my tree until we understand the problem Christian -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
