linux-kernel - Re: [PATCH v2 23/43] KVM: VMX: Use boolean returns for Posted Interrupt "test" helpers

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Date:   Thu, 28 Oct 2021 09:05:35 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Anup Patel <anup.patel@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Atish Patra <atish.patra@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        David Matlack <dmatlack@...gle.com>,
        Oliver Upton <oupton@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>
Subject: Re: [PATCH v2 23/43] KVM: VMX: Use boolean returns for Posted
 Interrupt "test" helpers

On Fri, 2021-10-08 at 19:12 -0700, Sean Christopherson wrote:
> Return bools instead of ints for the posted interrupt "test" helpers.
> The bit position of the flag being test does not matter to the callers,
> and is in fact lost by virtue of test_bit() itself returning a bool.
> 
> Returning ints is potentially dangerous, e.g. "pi_test_on(pi_desc) == 1"
> is safe-ish because ON is bit 0 and thus any sane implementation of
> pi_test_on() will work, but for SN (bit 1), checking "== 1" would rely on
> pi_test_on() to return 0 or 1, a.k.a. bools, as opposed to 0 or 2 (the
> positive bit position).
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/vmx/posted_intr.c | 4 ++--
>  arch/x86/kvm/vmx/posted_intr.h | 6 +++---
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
> index 6c2110d91b06..1688f8dc535a 100644
> --- a/arch/x86/kvm/vmx/posted_intr.c
> +++ b/arch/x86/kvm/vmx/posted_intr.c
> @@ -185,7 +185,7 @@ int pi_pre_block(struct kvm_vcpu *vcpu)
>  			   new.control) != old.control);
>  
>  	/* We should not block the vCPU if an interrupt is posted for it.  */
> -	if (pi_test_on(pi_desc) == 1)
> +	if (pi_test_on(pi_desc))
>  		__pi_post_block(vcpu);
>  
>  	local_irq_enable();
> @@ -216,7 +216,7 @@ void pi_wakeup_handler(void)
>  			blocked_vcpu_list) {
>  		struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
>  
> -		if (pi_test_on(pi_desc) == 1)
> +		if (pi_test_on(pi_desc))
>  			kvm_vcpu_kick(vcpu);
>  	}
>  	spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, cpu));
> diff --git a/arch/x86/kvm/vmx/posted_intr.h b/arch/x86/kvm/vmx/posted_intr.h
> index 7f7b2326caf5..36ae035f14aa 100644
> --- a/arch/x86/kvm/vmx/posted_intr.h
> +++ b/arch/x86/kvm/vmx/posted_intr.h
> @@ -40,7 +40,7 @@ static inline bool pi_test_and_clear_on(struct pi_desc *pi_desc)
>  			(unsigned long *)&pi_desc->control);
>  }
>  
> -static inline int pi_test_and_set_pir(int vector, struct pi_desc *pi_desc)
> +static inline bool pi_test_and_set_pir(int vector, struct pi_desc *pi_desc)
>  {
>  	return test_and_set_bit(vector, (unsigned long *)pi_desc->pir);
>  }
> @@ -74,13 +74,13 @@ static inline void pi_clear_sn(struct pi_desc *pi_desc)
>  		(unsigned long *)&pi_desc->control);
>  }
>  
> -static inline int pi_test_on(struct pi_desc *pi_desc)
> +static inline bool pi_test_on(struct pi_desc *pi_desc)
>  {
>  	return test_bit(POSTED_INTR_ON,
>  			(unsigned long *)&pi_desc->control);
>  }
>  
> -static inline int pi_test_sn(struct pi_desc *pi_desc)
> +static inline bool pi_test_sn(struct pi_desc *pi_desc)
>  {
>  	return test_bit(POSTED_INTR_SN,
>  			(unsigned long *)&pi_desc->control);
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky