2016-07-07 15:02 GMT+08:00 Haozhong Zhang <haozhong.zhang@xxxxxxxxx>: > On 07/07/16 14:56, Wanpeng Li wrote: >> 2016-07-07 14:48 GMT+08:00 Haozhong Zhang <haozhong.zhang@xxxxxxxxx>: >> > On 07/07/16 11:46, 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. >> >> >> >> Tested-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx> >> >> 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; >> > >> > If patch 2 can avoid accidentally enabling preemption timer in vmcs02, >> > will this one still be needed? >> >> After complete "L1 TSC deadline timer to trigger while L2 is running", >> L0's preemption timer fire when L2 is running can result in >> (is_guest_mode(vcpu) && nested_vmx_exit_handled(vcpu)) be true, right? >> > > In prepare_vmcs02(): > > exec_control &= ~PIN_BASED_VMX_PREEMPTION_TIMER; > ... > vmcs_write32(PIN_BASED_VM_EXEC_CONTROL, exec_control); > > so preemption timer will never be enabled while L2 guest is running. It is not true after Paolo's patch. Regards, Wanpeng Li -- 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
