Re: [PATCH] KVM: x86: refactor handling of MMIO page fault (cosmetic only)

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On 30/03/2018 00:41, Sean Christopherson wrote:
> Redo kvm_mmu_page_fault()'s interaction with handle_mmio_page_fault()
> so that the behavior of falling through to mmu.page_fault() when
> handle_mmio_page_fault() returns RET_PF_INVALID is more obvious.
> The current approach of setting and checking RET_PF_INVALID outside
> of the MMIO flow can lead readers to believe that RET_PF_INVALID
> may be used for something other than signifying that the MMIO generation
> has changed.
> 
> This is a purely cosmetic change, e.g. kvm.ko's kvm_mmu_page_fault
> is binary identical on my system before and after this patch
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> ---
>  arch/x86/kvm/mmu.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index f551962ac294..662bb448c7fc 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -4927,21 +4927,21 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code,
>  		vcpu->arch.gpa_val = cr2;
>  	}
>  
> -	r = RET_PF_INVALID;
>  	if (unlikely(error_code & PFERR_RSVD_MASK)) {
>  		r = handle_mmio_page_fault(vcpu, cr2, direct);
>  		if (r == RET_PF_EMULATE) {
>  			emulation_type = 0;
>  			goto emulate;
>  		}
> +		if (r != RET_PF_INVALID)
> +			goto pf_done;
>  	}
>  
> -	if (r == RET_PF_INVALID) {
> -		r = vcpu->arch.mmu.page_fault(vcpu, cr2, lower_32_bits(error_code),
> -					      false);
> -		WARN_ON(r == RET_PF_INVALID);
> -	}
> +	r = vcpu->arch.mmu.page_fault(vcpu, cr2, lower_32_bits(error_code),
> +				      false);
> +	WARN_ON(r == RET_PF_INVALID);
>  
> +pf_done:
>  	if (r == RET_PF_RETRY)
>  		return 1;
>  	if (r < 0)
> 

I don't know... The extra goto makes things a bit harder to read.  Maybe
moving the "emulate" label to a separate function can make things more
bearable, but I'm not sure about that either.  For now I'm not applying
the patch.

Paolo



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