Re: [Qemu-devel] freeze host when injecting NMIs in the guest, at least in 4.4-rc4+

[Paolo Bonzini]

On 10/12/2015 17:53, Borislav Petkov wrote:
> Just did, there it splats even when booting the guest, without even
> injecting NMIs:
> 
> [  113.233992] ===============================
> [  113.238192] [ INFO: suspicious RCU usage. ]
> [  113.242393] 4.4.0-rc4+ #1 Not tainted
> [  113.246056] -------------------------------
> [  113.250257] arch/x86/kvm/trace.h:29 suspicious rcu_dereference_check() 
> usage!
> [  113.257400] 
>                other info that might help us debug this:
> 
> [  113.265432] 
>                RCU used illegally from idle CPU!
>                rcu_scheduler_active = 1, debug_locks = 0
> [  113.276321] RCU used illegally from extended quiescent state!
> [  113.282083] 1 lock held by qemu-system-x86/2275:
> [  113.286711]  #0:  (&vcpu->mutex){+.+.+.}, at: [<ffffffffa01d472c>] 
> vcpu_load+0x1c/0x80 [kvm]
> [  113.295270] 
>                stack backtrace:
> [  113.299644] CPU: 4 PID: 2275 Comm: qemu-system-x86 Not tainted 4.4.0-rc4+ 
> #1
> [  113.306706] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A13 
> 05/11/2014
> [  113.314122]  0000000000000001 ffff88042f263d28 ffffffff813c2cfc 
> ffff880432d53000
> [  113.321575]  ffff88042f263d58 ffffffff810c5157 ffff88042f268000 
> 0000000000000000
> [  113.329027]  0000000000000000 0000000000000001 ffff88042f263e10 
> ffffffffa01ee7c8
> [  113.336483] Call Trace:
> [  113.338939]  [<ffffffff813c2cfc>] dump_stack+0x4e/0x82
> [  113.344098]  [<ffffffff810c5157>] lockdep_rcu_suspicious+0xe7/0x120
> [  113.350385]  [<ffffffffa01ee7c8>] kvm_arch_vcpu_ioctl_run+0x16f8/0x19c0 
> [kvm]
> [  113.357544]  [<ffffffffa01ed1a0>] ? kvm_arch_vcpu_ioctl_run+0xd0/0x19c0 
> [kvm]
> [  113.364695]  [<ffffffffa01d4b32>] kvm_vcpu_ioctl+0x342/0x700 [kvm]
> [  113.370896]  [<ffffffff810c4a7d>] ? __lock_is_held+0x4d/0x70
> [  113.376583]  [<ffffffff812351ae>] ? __fget+0xfe/0x200
> [  113.381662]  [<ffffffff812291f1>] do_vfs_ioctl+0x301/0x550
> [  113.387156]  [<ffffffff8123531a>] ? __fget_light+0x2a/0x90
> [  113.392654]  [<ffffffff81229481>] SyS_ioctl+0x41/0x70
> [  113.397739]  [<ffffffff8185cb36>] entry_SYSCALL_64_fastpath+0x16/0x7a
> [  113.755008] kvm: zapping shadow pages for mmio generation wraparound

Wow, this must have been there forever...

Paolo