linux-kernel - Re: [RESEND PATCH 03/13] KVM: x86: Refactor kvm_vcpu_do

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Date:   Fri, 23 Aug 2019 16:05:17 +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 03/13] KVM: x86: Refactor kvm_vcpu_do_singlestep()
 to remove out param



> On 23 Aug 2019, at 4:06, Sean Christopherson <sean.j.christopherson@...el.com> 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.
> 
> 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);
> -- 
> 2.22.0
> 

Reviewed-by: Liran Alon <liran.alon@...cle.com>

-Liran