Re: [RFC PATCH 3/3] KVM: x86: Use KVM_BUG/KVM_BUG_ON to handle bugs that are fatal to the VM

[Vitaly Kuznetsov]

Sean Christopherson <sean.j.christopherson@xxxxxxxxx> writes:

> Add support for KVM_REQ_VM_BUGG in x86, and replace a variety of WARNs
> with KVM_BUG() and KVM_BUG_ON().  Return -EIO if a KVM_BUG is hit to
> align with the common KVM behavior of rejecting iocts() with -EIO if the
> VM is bugged.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> ---
>  arch/x86/kvm/svm/svm.c |  2 +-
>  arch/x86/kvm/vmx/vmx.c | 23 ++++++++++++++---------
>  arch/x86/kvm/x86.c     |  4 ++++
>  3 files changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 3da5b2f1b4a1..e684794c6249 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1380,7 +1380,7 @@ static void svm_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
>  		load_pdptrs(vcpu, vcpu->arch.walk_mmu, kvm_read_cr3(vcpu));
>  		break;
>  	default:
> -		WARN_ON_ONCE(1);
> +		KVM_BUG_ON(1, vcpu->kvm);
>  	}
>  }
>  
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 6f9a0c6d5dc5..810d46ab0a47 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2250,7 +2250,7 @@ static void vmx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
>  		vcpu->arch.cr4 |= vmcs_readl(GUEST_CR4) & guest_owned_bits;
>  		break;
>  	default:
> -		WARN_ON_ONCE(1);
> +		KVM_BUG_ON(1, vcpu->kvm);
>  		break;
>  	}
>  }
> @@ -4960,6 +4960,7 @@ static int handle_cr(struct kvm_vcpu *vcpu)
>  			return kvm_complete_insn_gp(vcpu, err);
>  		case 3:
>  			WARN_ON_ONCE(enable_unrestricted_guest);
> +
>  			err = kvm_set_cr3(vcpu, val);
>  			return kvm_complete_insn_gp(vcpu, err);
>  		case 4:
> @@ -4985,14 +4986,13 @@ static int handle_cr(struct kvm_vcpu *vcpu)
>  		}
>  		break;
>  	case 2: /* clts */
> -		WARN_ONCE(1, "Guest should always own CR0.TS");
> -		vmx_set_cr0(vcpu, kvm_read_cr0_bits(vcpu, ~X86_CR0_TS));
> -		trace_kvm_cr_write(0, kvm_read_cr0(vcpu));
> -		return kvm_skip_emulated_instruction(vcpu);
> +		KVM_BUG(1, vcpu->kvm, "Guest always owns CR0.TS");
> +		return -EIO;
>  	case 1: /*mov from cr*/
>  		switch (cr) {
>  		case 3:
>  			WARN_ON_ONCE(enable_unrestricted_guest);
> +

Here, were you intended to replace WARN_ON_ONCE() with KVM_BUG_ON() or
this is just a stray newline added?

>  			val = kvm_read_cr3(vcpu);
>  			kvm_register_write(vcpu, reg, val);
>  			trace_kvm_cr_read(cr, val);
> @@ -5330,7 +5330,9 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
>  
>  static int handle_nmi_window(struct kvm_vcpu *vcpu)
>  {
> -	WARN_ON_ONCE(!enable_vnmi);
> +	if (KVM_BUG_ON(!enable_vnmi, vcpu->kvm))
> +		return -EIO;
> +
>  	exec_controls_clearbit(to_vmx(vcpu), CPU_BASED_NMI_WINDOW_EXITING);
>  	++vcpu->stat.nmi_window_exits;
>  	kvm_make_request(KVM_REQ_EVENT, vcpu);
> @@ -5908,7 +5910,8 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
>  	 * below) should never happen as that means we incorrectly allowed a
>  	 * nested VM-Enter with an invalid vmcs12.
>  	 */
> -	WARN_ON_ONCE(vmx->nested.nested_run_pending);
> +	if (KVM_BUG_ON(vmx->nested.nested_run_pending, vcpu->kvm))
> +		return -EIO;
>  
>  	/* If guest state is invalid, start emulating */
>  	if (vmx->emulation_required)
> @@ -6258,7 +6261,9 @@ static int vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
>  	int max_irr;
>  	bool max_irr_updated;
>  
> -	WARN_ON(!vcpu->arch.apicv_active);
> +	if (KVM_BUG_ON(!vcpu->arch.apicv_active, vcpu->kvm))
> +		return -EIO;
> +
>  	if (pi_test_on(&vmx->pi_desc)) {
>  		pi_clear_on(&vmx->pi_desc);
>  		/*
> @@ -6345,7 +6350,7 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
>  	gate_desc *desc;
>  	u32 intr_info = vmx_get_intr_info(vcpu);
>  
> -	if (WARN_ONCE(!is_external_intr(intr_info),
> +	if (KVM_BUG(!is_external_intr(intr_info), vcpu->kvm,
>  	    "KVM: unexpected VM-Exit interrupt info: 0x%x", intr_info))
>  		return;
>  
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 17f4995e80a7..672eb5142b34 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8363,6 +8363,10 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  	bool req_immediate_exit = false;
>  
>  	if (kvm_request_pending(vcpu)) {
> +		if (kvm_check_request(KVM_REQ_VM_BUGGED, vcpu)) {

Do we want to allow userspace to continue executing the guest or should
we make KVM_REQ_VM_BUGGED permanent by replacing kvm_check_request()
with kvm_test_request()?

> +			r = -EIO;
> +			goto out;
> +		}
>  		if (kvm_check_request(KVM_REQ_GET_VMCS12_PAGES, vcpu)) {
>  			if (unlikely(!kvm_x86_ops.nested_ops->get_vmcs12_pages(vcpu))) {
>  				r = 0;

-- 
Vitaly