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

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Date:   Fri, 7 Jun 2019 15:42:31 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] KVM: arm64: Drop 'const' from argument of vq_present()

On Fri, Jun 07, 2019 at 11:30:37AM +0530, Viresh Kumar wrote:
> On 04-06-19, 10:59, Dave Martin wrote:
> > 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?
> 
> I will send a patch with that if that's what you want.

I think this would solve the problem and simplify the code a bit at the
same time.

So go for it.

Cheers
---Dave