linux-kernel - Re: [PATCH V2] KVM: arm64: Implement vq

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Date:   Mon, 10 Jun 2019 10:09:21 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry@....com>,
        Suzuki K Pouloze <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] KVM: arm64: Implement vq_present() as a macro

On Mon, Jun 10, 2019 at 11:36:33AM +0530, Viresh Kumar wrote:
> This routine is a one-liner and doesn't really need to be function and
> should be rather implemented as a macro.
> 
> Suggested-by: Dave Martin <Dave.Martin@....com>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> V1->V2:
> - The previous implementation was fixing a compilation error that
>   occurred only with old compilers (from 2015) due to a bug in the
>   compiler itself.
> 
> - Dave suggested to rather implement this as a macro which made more
>   sense.
> 
>  arch/arm64/kvm/guest.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 3ae2f82fca46..a429ed36a6a0 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -207,13 +207,7 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>  
>  #define vq_word(vq) (((vq) - SVE_VQ_MIN) / 64)
>  #define vq_mask(vq) ((u64)1 << ((vq) - SVE_VQ_MIN) % 64)
> -
> -static bool vq_present(
> -	const u64 (*const vqs)[KVM_ARM64_SVE_VLS_WORDS],
> -	unsigned int vq)
> -{
> -	return (*vqs)[vq_word(vq)] & vq_mask(vq);
> -}
> +#define vq_present(vqs, vq) ((*(vqs))[vq_word(vq)] & vq_mask(vq))

You could drop the extra level of indirection on vqs now.  The only
thing it achieves is to enforce the size of the array via type-
checkout, but the macro can't easily do that (unless you can think
of another way to do it).

Otherwise, looks good.

Cheers
---Dave