linux-kernel - Re: [PATCH 2/3] KVM: x86: use kvm_complete_insn

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Date:   Mon, 14 Dec 2020 14:52:09 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Alexander Graf <graf@...zon.com>
Subject: Re: [PATCH 2/3] KVM: x86: use kvm_complete_insn_gp in emulating
 RDMSR/WRMSR

On 12/14/20 12:32 PM, Paolo Bonzini wrote:
> Simplify the four functions that handle {kernel,user} {rd,wr}msr, there
> is still some repetition between the two instances of rdmsr but the
> whole business of calling kvm_inject_gp and kvm_skip_emulated_instruction
> can be unified nicely.
> 
> Because complete_emulated_wrmsr now becomes essentially a call to
> kvm_complete_insn_gp, remove complete_emulated_msr.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Just two minor nits below.

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a3fdc16cfd6f..2f1bc52e70c0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1634,27 +1634,20 @@ int kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data)
>  }
>  EXPORT_SYMBOL_GPL(kvm_set_msr);
>  
>  
>  	/* MSR read failed? Inject a #GP */

This comment isn't accurate any more, maybe just delete it?

> -	if (r) {
> +	if (!r) {
> +		trace_kvm_msr_read(ecx, data);
> +
> +		kvm_rax_write(vcpu, data & -1u);
> +		kvm_rdx_write(vcpu, (data >> 32) & -1u);
> +	} else {
>  		trace_kvm_msr_read_ex(ecx);
> -		kvm_inject_gp(vcpu, 0);
> -		return 1;
>  	}
>  
> -	trace_kvm_msr_read(ecx, data);
> -
> -	kvm_rax_write(vcpu, data & -1u);
> -	kvm_rdx_write(vcpu, (data >> 32) & -1u);
> -	return kvm_skip_emulated_instruction(vcpu);
> +	return kvm_complete_insn_gp(vcpu, r);
>  }
>  EXPORT_SYMBOL_GPL(kvm_emulate_rdmsr);
>  
> @@ -1750,14 +1742,12 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
>  		return r;
>  
>  	/* MSR write failed? Inject a #GP */

Ditto on this comment.

Thanks,
Tom

> -	if (r > 0) {
> +	if (!r)
> +		trace_kvm_msr_write(ecx, data);
> +	else
>  		trace_kvm_msr_write_ex(ecx, data);
> -		kvm_inject_gp(vcpu, 0);
> -		return 1;
> -	}
>  
> -	trace_kvm_msr_write(ecx, data);
> -	return kvm_skip_emulated_instruction(vcpu);
> +	return kvm_complete_insn_gp(vcpu, r);
>  }
>  EXPORT_SYMBOL_GPL(kvm_emulate_wrmsr);
>  
>