On 07/07/16 15:07, Wanpeng Li wrote: > 2016-07-07 15:02 GMT+08:00 Haozhong Zhang <haozhong.zh...@intel.com>: > > On 07/07/16 14:56, Wanpeng Li wrote: > >> 2016-07-07 14:48 GMT+08:00 Haozhong Zhang <haozhong.zh...@intel.com>: > >> > On 07/07/16 11:46, Wanpeng Li wrote: > >> >> From: Wanpeng Li <wanpeng...@hotmail.com> > >> >> > >> >> 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.zh...@intel.com> > >> >> Cc: Paolo Bonzini <pbonz...@redhat.com> > >> >> Cc: Radim Krčmář <rkrc...@redhat.com> > >> >> Cc: Yunhong Jiang <yunhong.ji...@intel.com> > >> >> Cc: Jan Kiszka <jan.kis...@siemens.com> > >> >> Cc: Haozhong Zhang <haozhong.zh...@intel.com> > >> >> Signed-off-by: Wanpeng Li <wanpeng...@hotmail.com> > >> >> --- > >> >> 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. >
OK, I didn't quite follow discussions before v3 and just noticed Paolo's patch in v2 comments is to enable L1 preemption timer while L2 is running. Then this one looks reasonable. Thanks, Haozhong
