linux-kernel - Re: [PATCH v2 03/14] KVM: x86: Refactor kvm_vcpu_do

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Date:   Tue, 17 Sep 2019 17:07:18 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Cc:     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, Liran Alon <liran.alon@...cle.com>
Subject: Re: [PATCH v2 03/14] KVM: x86: Refactor kvm_vcpu_do_singlestep() to
 remove out param

On 27/08/19 23:40, Sean Christopherson wrote:
> Return the single-step emulation result directly instead of via an out
> param.  Presumably at some point in the past kvm_vcpu_do_singlestep()
> could be called with *r==EMULATE_USER_EXIT, but that is no longer the
> case, i.e. all callers are happy to overwrite their own return variable.

It was actually done for consistency with kvm_vcpu_check_breakpoint.
It's okay to change it.

Paolo

> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Reviewed-by: Liran Alon <liran.alon@...cle.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/x86.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c6de5bc4fa5e..fe847f8eb947 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6377,7 +6377,7 @@ static int kvm_vcpu_check_hw_bp(unsigned long addr, u32 type, u32 dr7,
>  	return dr6;
>  }
>  
> -static void kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu, int *r)
> +static int kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_run *kvm_run = vcpu->run;
>  
> @@ -6386,10 +6386,10 @@ static void kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu, int *r)
>  		kvm_run->debug.arch.pc = vcpu->arch.singlestep_rip;
>  		kvm_run->debug.arch.exception = DB_VECTOR;
>  		kvm_run->exit_reason = KVM_EXIT_DEBUG;
> -		*r = EMULATE_USER_EXIT;
> -	} else {
> -		kvm_queue_exception_p(vcpu, DB_VECTOR, DR6_BS);
> +		return EMULATE_USER_EXIT;
>  	}
> +	kvm_queue_exception_p(vcpu, DB_VECTOR, DR6_BS);
> +	return EMULATE_DONE;
>  }
>  
>  int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu)
> @@ -6410,7 +6410,7 @@ int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu)
>  	 * that sets the TF flag".
>  	 */
>  	if (unlikely(rflags & X86_EFLAGS_TF))
> -		kvm_vcpu_do_singlestep(vcpu, &r);
> +		r = kvm_vcpu_do_singlestep(vcpu);
>  	return r == EMULATE_DONE;
>  }
>  EXPORT_SYMBOL_GPL(kvm_skip_emulated_instruction);
> @@ -6613,7 +6613,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
>  		vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
>  		kvm_rip_write(vcpu, ctxt->eip);
>  		if (r == EMULATE_DONE && ctxt->tf)
> -			kvm_vcpu_do_singlestep(vcpu, &r);
> +			r = kvm_vcpu_do_singlestep(vcpu);
>  		if (!ctxt->have_exception ||
>  		    exception_type(ctxt->exception.vector) == EXCPT_TRAP)
>  			__kvm_set_rflags(vcpu, ctxt->eflags);
>