linux-kernel - Re: [PATCH 1/2] KVM: nVMX: Fix nested #PF intends to break L1's vmlauch/vmresume

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Date:   Thu, 14 Sep 2017 19:58:20 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH 1/2] KVM: nVMX: Fix nested #PF intends to break L1's vmlauch/vmresume

2017-09-14 7:14 GMT+08:00 Wanpeng Li <kernellwp@...il.com>:
> 2017-09-14 5:45 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>> On 13/09/2017 13:03, Wanpeng Li wrote:
>>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>>
>>> ------------[ cut here ]------------
>>>  WARNING: CPU: 4 PID: 5280 at /home/kernel/linux/arch/x86/kvm//vmx.c:11394 nested_vmx_vmexit+0xc2b/0xd70 [kvm_intel]
>>>  CPU: 4 PID: 5280 Comm: qemu-system-x86 Tainted: G        W  OE   4.13.0+ #17
>>>  RIP: 0010:nested_vmx_vmexit+0xc2b/0xd70 [kvm_intel]
>>>  Call Trace:
>>>   ? emulator_read_emulated+0x15/0x20 [kvm]
>>>   ? segmented_read+0xae/0xf0 [kvm]
>>>   vmx_inject_page_fault_nested+0x60/0x70 [kvm_intel]
>>>   ? vmx_inject_page_fault_nested+0x60/0x70 [kvm_intel]
>>>   x86_emulate_instruction+0x733/0x810 [kvm]
>>>   vmx_handle_exit+0x2f4/0xda0 [kvm_intel]
>>>   ? kvm_arch_vcpu_ioctl_run+0xd2f/0x1c60 [kvm]
>>>   kvm_arch_vcpu_ioctl_run+0xdab/0x1c60 [kvm]
>>>   ? kvm_arch_vcpu_load+0x62/0x230 [kvm]
>>>   kvm_vcpu_ioctl+0x340/0x700 [kvm]
>>>   ? kvm_vcpu_ioctl+0x340/0x700 [kvm]
>>>   ? __fget+0xfc/0x210
>>>   do_vfs_ioctl+0xa4/0x6a0
>>>   ? __fget+0x11d/0x210
>>>   SyS_ioctl+0x79/0x90
>>>   entry_SYSCALL_64_fastpath+0x23/0xc2
>>>
>>> A nested #PF is triggered during L0 emulating instruction for L2. However, it
>>> doesn't consider we should not break L1's vmlauch/vmresme. This patch fixes
>>> it by queuing the #PF exception instead ,requesting an immediate VM exit from
>>> L2 and keeping the exception for L1 pending for a subsequent nested VM exit.
>>>
>>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>>> ---
>>>  arch/x86/kvm/vmx.c | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>> index 4253ade..fda9dd6 100644
>>> --- a/arch/x86/kvm/vmx.c
>>> +++ b/arch/x86/kvm/vmx.c
>>> @@ -9829,7 +9829,8 @@ static void vmx_inject_page_fault_nested(struct kvm_vcpu *vcpu,
>>>
>>>       WARN_ON(!is_guest_mode(vcpu));
>>>
>>> -     if (nested_vmx_is_page_fault_vmexit(vmcs12, fault->error_code)) {
>>> +     if (nested_vmx_is_page_fault_vmexit(vmcs12, fault->error_code) &&
>>> +             !to_vmx(vcpu)->nested.nested_run_pending) {
>>>               vmcs12->vm_exit_intr_error_code = fault->error_code;
>>>               nested_vmx_vmexit(vcpu, EXIT_REASON_EXCEPTION_NMI,
>>>                                 PF_VECTOR | INTR_TYPE_HARD_EXCEPTION |
>>>
>>
>> Is vmx_inject_page_fault_nested even needed at all these days?
>>
>> kvm_inject_page_fault's call to kvm_queue_exception_e should transform
>> into an L2->L1 vmexit when vmx_check_nested_events is called.
>
> I saw L0 reboot/hang after do something like below:

Maybe something associated with which commit ef54bcfee (KVM: x86: skip
writeback on injection of nested exception) pointed out, IIUC,
fault->nested_page_fault will not be changed in
vmx_inject_page_fault_nested(), so we always return false in the case
of vcpu->arch.nested.mmu.inject_page_fault(), then the issue which the
commit try to avoid is encountered.

Regards,
Wanpeng Li

>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 4253ade..96b4f6f 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -9822,24 +9822,6 @@ static bool
> nested_vmx_is_page_fault_vmexit(struct vmcs12 *vmcs12,
>         return inequality ^ bit;
>  }
>
> -static void vmx_inject_page_fault_nested(struct kvm_vcpu *vcpu,
> -               struct x86_exception *fault)
> -{
> -       struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> -
> -       WARN_ON(!is_guest_mode(vcpu));
> -
> -       if (nested_vmx_is_page_fault_vmexit(vmcs12, fault->error_code)) {
> -               vmcs12->vm_exit_intr_error_code = fault->error_code;
> -               nested_vmx_vmexit(vcpu, EXIT_REASON_EXCEPTION_NMI,
> -                                 PF_VECTOR | INTR_TYPE_HARD_EXCEPTION |
> -                                 INTR_INFO_DELIVER_CODE_MASK |
> INTR_INFO_VALID_MASK,
> -                                 fault->address);
> -       } else {
> -               kvm_inject_page_fault(vcpu, fault);
> -       }
> -}
> -
>  static inline bool nested_vmx_merge_msr_bitmap(struct kvm_vcpu *vcpu,
>                                                struct vmcs12 *vmcs12);
>
> @@ -10654,7 +10636,7 @@ static int prepare_vmcs02(struct kvm_vcpu
> *vcpu, struct vmcs12 *vmcs12,
>                 return 1;
>
>         if (!enable_ept)
> -               vcpu->arch.walk_mmu->inject_page_fault =
> vmx_inject_page_fault_nested;
> +               vcpu->arch.walk_mmu->inject_page_fault = kvm_inject_page_fault;
>
>         /*
>
> Regards,
> Wanpeng Li