Re: [PATCH v2] KVM: nVMX: Fix exception injection

From: Paolo Bonzini
Date: Mon Jun 05 2017 - 08:27:01 EST




On 05/06/2017 14:19, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> WARNING: CPU: 3 PID: 2840 at arch/x86/kvm/vmx.c:10966 nested_vmx_vmexit+0xdcd/0xde0 [kvm_intel]
> CPU: 3 PID: 2840 Comm: qemu-system-x86 Tainted: G OE 4.12.0-rc3+ #23
> RIP: 0010:nested_vmx_vmexit+0xdcd/0xde0 [kvm_intel]
> Call Trace:
> ? kvm_check_async_pf_completion+0xef/0x120 [kvm]
> ? rcu_read_lock_sched_held+0x79/0x80
> vmx_queue_exception+0x104/0x160 [kvm_intel]
> ? vmx_queue_exception+0x104/0x160 [kvm_intel]
> kvm_arch_vcpu_ioctl_run+0x1171/0x1ce0 [kvm]
> ? kvm_arch_vcpu_load+0x47/0x240 [kvm]
> ? kvm_arch_vcpu_load+0x62/0x240 [kvm]
> kvm_vcpu_ioctl+0x384/0x7b0 [kvm]
> ? kvm_vcpu_ioctl+0x384/0x7b0 [kvm]
> ? __fget+0xf3/0x210
> do_vfs_ioctl+0xa4/0x700
> ? __fget+0x114/0x210
> SyS_ioctl+0x79/0x90
> do_syscall_64+0x81/0x220
> entry_SYSCALL64_slow_path+0x25/0x25
>
> This is triggered occasionally by running both win7 and win2016 in L2, in
> addition, EPT is disabled on both L1 and L2. It can't be reproduced easily.
>
> Commit 0b6ac343fc (KVM: nVMX: Correct handling of exception injection) mentioned
> that "KVM wants to inject page-faults which it got to the guest. This function
> assumes it is called with the exit reason in vmcs02 being a #PF exception".
> Commit e011c663 (KVM: nVMX: Check all exceptions for intercept during delivery to
> L2) allows to check all exceptions for intercept during delivery to L2. However,
> there is no guarantee the exit reason is exception currently, when there is an
> external interrupt occurred on host, maybe a time interrupt for host which should
> not be injected to guest, and somewhere queues an exception, then the function
> nested_vmx_check_exception() will be called and the vmexit emulation codes will
> try to emulate the "Acknowledge interrupt on exit" behavior, the warning is
> triggered.
>
> This patch fixes it by confirming to inject exception to the guest when the exit
> reason in vmcs02 is exception.

I think the final part of the commit message needs to be reworded, like:

Reusing the exit reason from the L2->L0 vmexit is wrong in this case,
the reason must always be EXCEPTION_NMI when injecting an exception into
L1 as a nested vmexit.

Radim can fix it when applying.

Paolo

> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
> v1 -> v2:
> * pass EXIT_REASON_EXCEPTION_NMI instead of reusing to_vmx(vcpu)->exit_reason
>
> arch/x86/kvm/vmx.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 9b4b5d6..ca5d2b9 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2425,7 +2425,7 @@ static int nested_vmx_check_exception(struct kvm_vcpu *vcpu, unsigned nr)
> if (!(vmcs12->exception_bitmap & (1u << nr)))
> return 0;
>
> - nested_vmx_vmexit(vcpu, to_vmx(vcpu)->exit_reason,
> + nested_vmx_vmexit(vcpu, EXIT_REASON_EXCEPTION_NMI,
> vmcs_read32(VM_EXIT_INTR_INFO),
> vmcs_readl(EXIT_QUALIFICATION));
> return 1;
>