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

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Message-ID: <a179c573-334c-e075-199b-78a6ed06e26e@redhat.com>
Date:   Wed, 13 Sep 2017 23:45:48 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     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

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.

Paolo