On Wed, Jan 09, 2019 at 04:03:16PM +0100, Mike Galbraith wrote: > On Wed, 2019-01-09 at 15:42 +0100, Adam Borowski wrote: > > On Wed, Jan 09, 2019 at 06:38:58AM +0100, Mike Galbraith wrote: > > > KVM seems to be busted in master ATM. All I have to do to have host > > > start screaming and maybe exploding (if the guest doesn't do so first) > > > is to try to install a (obese in this case) kernel over nfs mount of > > > the host in a guest. > > > > > > Kernel producing the spew below is 3bd6e94, config attached. > > > > I get same, except that the BUGs were preceded by a bunch of warnings, > > Yeah, I was in too much of a rush... > > > > homer: # grep BUG: /netconsole.log > > > [ 1531.909703] BUG: Bad page state in process X pfn:100491 > > > [ 1531.958141] BUG: Bad page state in process systemd-journal pfn:100412 > > > [ 1532.662359] BUG: Bad page state in process X pfn:10043f > > > [ 1532.664033] BUG: Bad page state in process X pfn:10044d > > > [ 1532.686433] BUG: Bad page state in process systemd-journal pfn:1027b0 > > > > the first one being: > > > > Jan 9 00:41:22 umbar kernel: [74122.790461] WARNING: CPU: 2 PID: 26769 at > > arch/x86/kvm/mmu.c:830 mmu_spte_clear_track_bits+0x7e/0x100 > > ...I also get oodles of those.
There's also a bugzilla bug that's probably the same thing: https://bugzilla.kernel.org/show_bug.cgi?id=202189. I'm 99.9% confident this is only manifests when reclaiming from the guest, i.e. host is swapping out a VM's memory. The WARNING is complaining that KVM is trying to reclaim a page before it has been removed from KVM's MMU, i.e. a use-after-free scenario is imminent, and the stack trace shows the kernel is reclaming. The bug also listed host swapping as a possible requirement, and last but not least, I was only able to reproduce this by forcing reclaim. I'll try to bisect.
