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

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Message-ID: <CANRm+CyCLi-gCoYg75eFi=5ojij90wt6XgWkrUcfyWbpq_T8HQ@mail.gmail.com>
Date:   Fri, 15 Sep 2017 11:48:30 +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 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.

After more investigation, this will break the original goal of what
vmx_inject_page_fault_nested() tries to fix.
http://www.spinics.net/lists/kvm/msg96579.html

Regards,
Wanpeng Li