linux-kernel - Re: [RESEND PATCH 06/13] KVM: x86: Move #GP injection for VMware into x86_emulate

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Date:   Fri, 23 Aug 2019 16:30:34 +0300
From:   Liran Alon <liran.alon@...cle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH 06/13] KVM: x86: Move #GP injection for VMware into
 x86_emulate_instruction()



> On 23 Aug 2019, at 4:07, Sean Christopherson <sean.j.christopherson@...el.com> wrote:
> 
> Immediately inject a #GP when VMware emulation fails and return
> EMULATE_DONE instead of propagating EMULATE_FAIL up the stack.  This
> helps pave the way for removing EMULATE_FAIL altogether.
> 
> Rename EMULTYPE_VMWARE to EMULTYPE_VMWARE_GP to help document why a #GP
> is injected on emulation failure.

I would rephrase to say that this rename is in order to document that the x86 emulator is called to handle
VMware #GP interception. In theory, VMware could have also added weird behaviour
to #UD interception as-well. :P

Besides minor comments inline below:
Reviewed-by: Liran Alon <liran.alon@...cle.com>

-Liran

> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
> arch/x86/include/asm/kvm_host.h |  2 +-
> arch/x86/kvm/svm.c              |  9 ++-------
> arch/x86/kvm/vmx/vmx.c          |  9 ++-------
> arch/x86/kvm/x86.c              | 14 +++++++++-----
> 4 files changed, 14 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index dd6bd9ed0839..d1d5b5ca1195 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1318,7 +1318,7 @@ enum emulation_result {
> #define EMULTYPE_TRAP_UD	    (1 << 1)
> #define EMULTYPE_SKIP		    (1 << 2)
> #define EMULTYPE_ALLOW_RETRY	    (1 << 3)
> -#define EMULTYPE_VMWARE		    (1 << 5)
> +#define EMULTYPE_VMWARE_GP	    (1 << 5)
> int kvm_emulate_instruction(struct kvm_vcpu *vcpu, int emulation_type);
> int kvm_emulate_instruction_from_buffer(struct kvm_vcpu *vcpu,
> 					void *insn, int insn_len);
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index b96a119690f4..97562c2c8b7b 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -2768,7 +2768,6 @@ static int gp_interception(struct vcpu_svm *svm)
> {
> 	struct kvm_vcpu *vcpu = &svm->vcpu;
> 	u32 error_code = svm->vmcb->control.exit_info_1;
> -	int er;
> 
> 	WARN_ON_ONCE(!enable_vmware_backdoor);
> 
> @@ -2776,12 +2775,8 @@ static int gp_interception(struct vcpu_svm *svm)
> 		kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
> 		return 1;
> 	}
> -	er = kvm_emulate_instruction(vcpu, EMULTYPE_VMWARE);
> -	if (er == EMULATE_USER_EXIT)
> -		return 0;
> -	else if (er != EMULATE_DONE)
> -		kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
> -	return 1;
> +	return kvm_emulate_instruction(vcpu, EMULTYPE_VMWARE_GP) !=
> +						EMULATE_USER_EXIT;
> }
> 
> static bool is_erratum_383(void)
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 3ee0dd304bc7..25410c58c758 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -4492,7 +4492,6 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
> 	u32 intr_info, ex_no, error_code;
> 	unsigned long cr2, rip, dr6;
> 	u32 vect_info;
> -	enum emulation_result er;
> 
> 	vect_info = vmx->idt_vectoring_info;
> 	intr_info = vmx->exit_intr_info;
> @@ -4514,12 +4513,8 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
> 			kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
> 			return 1;
> 		}
> -		er = kvm_emulate_instruction(vcpu, EMULTYPE_VMWARE);
> -		if (er == EMULATE_USER_EXIT)
> -			return 0;
> -		else if (er != EMULATE_DONE)
> -			kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
> -		return 1;
> +		return kvm_emulate_instruction(vcpu, EMULTYPE_VMWARE_GP) !=
> +							EMULATE_USER_EXIT;
> 	}
> 
> 	/*
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e0f0e14d8fac..228ca71d5b01 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6210,8 +6210,10 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
> 	++vcpu->stat.insn_emulation_fail;
> 	trace_kvm_emulate_insn_failed(vcpu);
> 
> -	if (emulation_type & EMULTYPE_VMWARE)
> -		return EMULATE_FAIL;
> +	if (emulation_type & EMULTYPE_VMWARE_GP) {
> +		kvm_queue_exception_e(vcpu, GP_VECTOR, 0);

I would add here a comment explaining why you can assume #GP error-code is 0.
i.e. Explain that’s because VMware #GP interception is only related to IN{S}, OUT{S} and RDPMC
instructions which all of them raise #GP with error-code of 0.

> +		return EMULATE_DONE;
> +	}
> 
> 	kvm_queue_exception(vcpu, UD_VECTOR);
> 
> @@ -6543,9 +6545,11 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
> 		}
> 	}
> 
> -	if ((emulation_type & EMULTYPE_VMWARE) &&
> -	    !is_vmware_backdoor_opcode(ctxt))
> -		return EMULATE_FAIL;
> +	if ((emulation_type & EMULTYPE_VMWARE_GP) &&
> +	    !is_vmware_backdoor_opcode(ctxt)) {
> +		kvm_queue_exception_e(vcpu, GP_VECTOR, 0);

Same here.

> +		return EMULATE_DONE;
> +	}
> 
> 	if (emulation_type & EMULTYPE_SKIP) {
> 		kvm_rip_write(vcpu, ctxt->_eip);
> -- 
> 2.22.0
>