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Date: Thu, 10 Dec 2015 17:53:41 +0100
From: Borislav Petkov <bp@alien8.de>
Message-ID: <20151210165340.GA3831@pd.tnic>
References: <20151210140404.GA3049@nazgul.tnic> <20151210162733.GA6587@pd.tnic>
	<20151210164407.GA3593@nazgul.tnic> <5669AD06.3030409@redhat.com>
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Subject: Re: [Qemu-devel] freeze host when injecting NMIs in the guest,
 at least in 4.4-rc4+
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: lkml <linux-kernel@vger.kernel.org>, kvm@vger.kernel.org, qemu-devel@nongnu.org

On Thu, Dec 10, 2015 at 05:49:10PM +0100, Paolo Bonzini wrote:
> Can you try it on Intel?

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

-- 
Regards/Gruss,
    Boris.

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