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SubjectRe: [PATCH v3] KVM: nVMX: Fix incorrect preemption timer vmexit in nested guest
2016-07-06 21:26 GMT+08:00 Haozhong Zhang <haozhong.zhang@intel.com>:
> On 07/06/16 19:42, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@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.
>>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>> Cc: Yunhong Jiang <yunhong.jiang@intel.com>
>> Cc: Jan Kiszka <jan.kiszka@siemens.com>
>> Cc: Haozhong Zhang <haozhong.zhang@intel.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@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;
>> 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@intel.com>

Thanks. :)

Regards,
Wanpeng Li

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