linux-kernel - Re: [PATCH] KVM: arm64: Drop 'const' from argument of vq

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Date:   Tue, 4 Jun 2019 10:59:15 +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>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Drop 'const' from argument of vq_present()

On Tue, Jun 04, 2019 at 10:13:19AM +0530, Viresh Kumar wrote:
> We currently get following compilation warning:
> 
> arch/arm64/kvm/guest.c: In function 'set_sve_vls':
> arch/arm64/kvm/guest.c:262:18: warning: passing argument 1 of 'vq_present' from incompatible pointer type
> arch/arm64/kvm/guest.c:212:13: note: expected 'const u64 (* const)[8]' but argument is of type 'u64 (*)[8]'
> 
> The argument can't be const, as it is copied at runtime using
> copy_from_user(). Drop const from the prototype of vq_present().
> 
> Fixes: 9033bba4b535 ("KVM: arm64/sve: Add pseudo-register for the guest's vector lengths")
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  arch/arm64/kvm/guest.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 3ae2f82fca46..78f5a4f45e0a 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -209,7 +209,7 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>  #define vq_mask(vq) ((u64)1 << ((vq) - SVE_VQ_MIN) % 64)
>  
>  static bool vq_present(
> -	const u64 (*const vqs)[KVM_ARM64_SVE_VLS_WORDS],
> +	u64 (*const vqs)[KVM_ARM64_SVE_VLS_WORDS],
>  	unsigned int vq)
>  {
>  	return (*vqs)[vq_word(vq)] & vq_mask(vq);

Ack, but maybe this should just be converted to a macro?

It already feels a bit like overkill for this to be a function.

Cheers
---Dave