linux-kernel - Re: [PATCH 06/13] KVM: x86: pass the whole hflags field to emulator and back

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Date:	Tue, 05 May 2015 11:47:33 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	rkrcmar@...hat.com, guangrong.xiao@...ux.intel.com,
	Yang Zhang <yang.z.zhang@...el.com>, wanpeng.li@...ux.intel.com
Subject: Re: [PATCH 06/13] KVM: x86: pass the whole hflags field to emulator and back

Paolo Bonzini <pbonzini@...hat.com> writes:

> The hflags field will contain information about system management mode
> and will be useful for the emulator.  Pass the entire field rather than
> just the guest-mode information.

With respect to maintaining maximum isolation between vcpu internals and
the emulator, why not just "bool smm_mode" ?

> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/include/asm/kvm_emulate.h | 5 ++++-
>  arch/x86/kvm/emulate.c             | 6 +++---
>  arch/x86/kvm/x86.c                 | 4 +++-
>  3 files changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
> index 57a9d94fe160..7410879a41f7 100644
> --- a/arch/x86/include/asm/kvm_emulate.h
> +++ b/arch/x86/include/asm/kvm_emulate.h
> @@ -262,6 +262,9 @@ enum x86emul_mode {
>  	X86EMUL_MODE_PROT64,	/* 64-bit (long) mode.    */
>  };
>  
> +/* These match some of the HF_* flags defined in kvm_host.h  */
> +#define X86EMUL_GUEST_MASK           (1 << 5) /* VCPU is in guest-mode */
> +
>  struct x86_emulate_ctxt {
>  	const struct x86_emulate_ops *ops;
>  
> @@ -273,8 +276,8 @@ struct x86_emulate_ctxt {
>  
>  	/* interruptibility state, as a result of execution of STI or MOV SS */
>  	int interruptibility;
> +	int emul_flags;
>  
> -	bool guest_mode; /* guest running a nested guest */
>  	bool perm_ok; /* do not check permissions if true */
>  	bool ud;	/* inject an #UD if host doesn't support insn */
>  
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 630bcb0d7a04..cdb612b50910 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -4871,7 +4871,7 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
>  				fetch_possible_mmx_operand(ctxt, &ctxt->dst);
>  		}
>  
> -		if (unlikely(ctxt->guest_mode) && (ctxt->d & Intercept)) {
> +		if (unlikely(ctxt->emul_flags & X86EMUL_GUEST_MASK) && ctxt->intercept) {
>  			rc = emulator_check_intercept(ctxt, ctxt->intercept,
>  						      X86_ICPT_PRE_EXCEPT);
>  			if (rc != X86EMUL_CONTINUE)
> @@ -4900,7 +4900,7 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
>  				goto done;
>  		}
>  
> -		if (unlikely(ctxt->guest_mode) && (ctxt->d & Intercept)) {
> +		if (unlikely(ctxt->emul_flags & X86EMUL_GUEST_MASK) && (ctxt->d & Intercept)) {
>  			rc = emulator_check_intercept(ctxt, ctxt->intercept,
>  						      X86_ICPT_POST_EXCEPT);
>  			if (rc != X86EMUL_CONTINUE)
> @@ -4953,7 +4953,7 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
>  
>  special_insn:
>  
> -	if (unlikely(ctxt->guest_mode) && (ctxt->d & Intercept)) {
> +	if (unlikely(ctxt->emul_flags & X86EMUL_GUEST_MASK) && (ctxt->d & Intercept)) {
>  		rc = emulator_check_intercept(ctxt, ctxt->intercept,
>  					      X86_ICPT_POST_MEMACCESS);
>  		if (rc != X86EMUL_CONTINUE)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 856598afa6b4..6009e6a0e406 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5132,7 +5132,8 @@ static void init_emulate_ctxt(struct kvm_vcpu *vcpu)
>  		     (cs_l && is_long_mode(vcpu))	? X86EMUL_MODE_PROT64 :
>  		     cs_db				? X86EMUL_MODE_PROT32 :
>  							  X86EMUL_MODE_PROT16;
> -	ctxt->guest_mode = is_guest_mode(vcpu);
> +	BUILD_BUG_ON(HF_GUEST_MASK != X86EMUL_GUEST_MASK);
> +	ctxt->emul_flags = vcpu->arch.hflags;
>  
>  	init_decode_cache(ctxt);
>  	vcpu->arch.emulate_regs_need_sync_from_vcpu = false;
> @@ -5500,6 +5501,7 @@ restart:
>  		unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
>  		toggle_interruptibility(vcpu, ctxt->interruptibility);
>  		vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
> +		vcpu->arch.hflags = ctxt->emul_flags;
>  		kvm_rip_write(vcpu, ctxt->eip);
>  		if (r == EMULATE_DONE)
>  			kvm_vcpu_check_singlestep(vcpu, rflags, &r);
--
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