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SubjectRe: [PATCH v3] KVM: nVMX: Fix incorrect preemption timer vmexit in nested guest
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>

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