I believe this happens when the VMCS12 MSR bitmap address is valid, but no device is configured to respond to the bus request. I agree that the warning should be removed. However, in this case, the VMCS12 MSR bitmap should read as all 1s. The same is true everywhere that nested_get_page returns NULL. Reads should return all 1s and writes should be ignored. On Tue, Feb 28, 2017 at 11:06 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > Hello, > > I've got the following WARNING while running syzkaller fuzzer: > > ------------[ cut here ]------------ > WARNING: CPU: 0 PID: 7832 at arch/x86/kvm/vmx.c:9709 > nested_vmx_merge_msr_bitmap arch/x86/kvm/vmx.c:9709 [inline] > WARNING: CPU: 0 PID: 7832 at arch/x86/kvm/vmx.c:9709 > nested_get_vmcs12_pages+0xfb6/0x15c0 arch/x86/kvm/vmx.c:9640 > Kernel panic - not syncing: panic_on_warn set ... > CPU: 0 PID: 7832 Comm: syz-executor1 Not tainted 4.10.0+ #229 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:15 [inline] > dump_stack+0x2ee/0x3ef lib/dump_stack.c:51 > panic+0x1fb/0x412 kernel/panic.c:179 > __warn+0x1c4/0x1e0 kernel/panic.c:540 > warn_slowpath_null+0x2c/0x40 kernel/panic.c:583 > nested_vmx_merge_msr_bitmap arch/x86/kvm/vmx.c:9709 [inline] > nested_get_vmcs12_pages+0xfb6/0x15c0 arch/x86/kvm/vmx.c:9640 > enter_vmx_non_root_mode arch/x86/kvm/vmx.c:10471 [inline] > nested_vmx_run+0x6186/0xaab0 arch/x86/kvm/vmx.c:10561 > handle_vmlaunch+0x1a/0x20 arch/x86/kvm/vmx.c:7312 > vmx_handle_exit+0xfc0/0x3f00 arch/x86/kvm/vmx.c:8526 > vcpu_enter_guest arch/x86/kvm/x86.c:6982 [inline] > vcpu_run arch/x86/kvm/x86.c:7044 [inline] > kvm_arch_vcpu_ioctl_run+0x1418/0x4840 arch/x86/kvm/x86.c:7205 > kvm_vcpu_ioctl+0x673/0x1120 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2570 > sctp: [Deprecated]: syz-executor2 (pid 7865) Use of int in max_burst > socket option. > Use struct sctp_assoc_value instead > vfs_ioctl fs/ioctl.c:43 [inline] > do_vfs_ioctl+0x1bf/0x1790 fs/ioctl.c:683 > SYSC_ioctl fs/ioctl.c:698 [inline] > SyS_ioctl+0x8f/0xc0 fs/ioctl.c:689 > entry_SYSCALL_64_fastpath+0x1f/0xc2 > 9pnet_virtio: no channels available for device ./bus > RIP: 0033:0x4458d9 > RSP: 002b:00007f248b1abb58 EFLAGS: 00000286 ORIG_RAX: 0000000000000010 > RAX: ffffffffffffffda RBX: 000000000000001b RCX: 00000000004458d9 > RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 000000000000001b > RBP: 00000000006dfcd0 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000286 R12: 00000000007080a8 > R13: 000000000000001a R14: 000000000000001b R15: 00000000201b3000 > > > If I am reading this correctly, failure to map msr bitmap is trivially > trigger-able by guest (specify an invalid address?) and thus should > not be a warning. The case is already handled by disabling > acceleration. So can we remove the warning? or replace with pr_err?
