On 07/06/16 19:42, Wanpeng Li wrote: > From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> > > BUG: unable to handle kernel NULL pointer dereference at (null) > IP: [< (null)>] (null) > PGD 0 > Oops: 0010 [#1] SMP > Call Trace: > ? kvm_lapic_expired_hv_timer+0x47/0x90 [kvm] > handle_preemption_timer+0xe/0x20 [kvm_intel] > vmx_handle_exit+0x169/0x15a0 [kvm_intel] > ? kvm_arch_vcpu_ioctl_run+0xd5d/0x19d0 [kvm] > kvm_arch_vcpu_ioctl_run+0xdee/0x19d0 [kvm] > ? kvm_arch_vcpu_ioctl_run+0xd5d/0x19d0 [kvm] > ? vcpu_load+0x1c/0x60 [kvm] > ? kvm_arch_vcpu_load+0x57/0x260 [kvm] > kvm_vcpu_ioctl+0x2d3/0x7c0 [kvm] > do_vfs_ioctl+0x96/0x6a0 > ? __fget_light+0x2a/0x90 > SyS_ioctl+0x79/0x90 > do_syscall_64+0x68/0x180 > entry_SYSCALL64_slow_path+0x25/0x25 > Code: Bad RIP value. > RIP [< (null)>] (null) > RSP <ffff8800b5263c48> > CR2: 0000000000000000 > ---[ end trace 9c70c48b1a2bc66e ]--- > > This can be reproduced readily by preemption timer enabled on L0 and disabled > on L1. > > Preemption timer for nested VMX is emulated by hrtimer which is started on L2 > entry, stopped on L2 exit and evaluated via the check_nested_events hook. However, > nested_vmx_exit_handled is always return true for preemption timer vmexit, then > the L1 preemption timer vmexit is captured and be treated as a L2 preemption > timer vmexit, incurr a nested vmexit dereference NULL pointer. > > This patch fix it by depending on check_nested_events to capture L2 preemption > timer(emulated hrtimer) expire and nested vmexit. > > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> > Cc: Yunhong Jiang <yunhong.jiang@xxxxxxxxx> > Cc: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> > Cc: Haozhong Zhang <haozhong.zhang@xxxxxxxxx> > Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> > --- > v2 -> v3: > * update patch subject > v1 -> v2: > * fix typo in patch description > > arch/x86/kvm/vmx.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index 85e2f0a..29c16a8 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -8041,6 +8041,8 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu) > return nested_cpu_has2(vmcs12, SECONDARY_EXEC_XSAVES); > case EXIT_REASON_PCOMMIT: > return nested_cpu_has2(vmcs12, SECONDARY_EXEC_PCOMMIT); > + case EXIT_REASON_PREEMPTION_TIMER: > + return false; > default: > return true; > } > -- > 1.9.1 > This patch also fixed the crash of L1 Xen with L2 HVM guest. Xen does not enable preemption timer for HVM guests, and will get panic if it receives a preemption timer vmexit. Tested-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx> -- 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
