linux-kernel - Re: [PATCH v4 1/8] KVM: arm64: vgic-v3: Fix some error codes when setting RDIST base

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Message-ID: <87wntmp99c.wl-maz@kernel.org>
Date:   Thu, 01 Apr 2021 11:52:15 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        drjones@...hat.com, alexandru.elisei@....com, james.morse@....com,
        suzuki.poulose@....com, shuah@...nel.org, pbonzini@...hat.com
Subject: Re: [PATCH v4 1/8] KVM: arm64: vgic-v3: Fix some error codes when setting RDIST base

Hi Eric,

On Thu, 01 Apr 2021 09:52:31 +0100,
Eric Auger <eric.auger@...hat.com> wrote:
> 
> KVM_DEV_ARM_VGIC_GRP_ADDR group doc says we should return
> -EEXIST in case the base address of the redist is already set.
> We currently return -EINVAL.
> 
> However we need to return -EINVAL in case a legacy REDIST address
> is attempted to be set while REDIST_REGIONS were set. This case
> is discriminated by looking at the count field.
> 
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> 
> ---
> 
> v1 -> v2:
> - simplify the check sequence
> ---
>  arch/arm64/kvm/vgic/vgic-mmio-v3.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> index 15a6c98ee92f0..013b737b658f8 100644
> --- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> +++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> @@ -791,10 +791,6 @@ static int vgic_v3_insert_redist_region(struct kvm *kvm, uint32_t index,
>  	size_t size = count * KVM_VGIC_V3_REDIST_SIZE;
>  	int ret;
>  
> -	/* single rdist region already set ?*/
> -	if (!count && !list_empty(rd_regions))
> -		return -EINVAL;
> -
>  	/* cross the end of memory ? */
>  	if (base + size < base)
>  		return -EINVAL;
> @@ -805,11 +801,14 @@ static int vgic_v3_insert_redist_region(struct kvm *kvm, uint32_t index,
>  	} else {
>  		rdreg = list_last_entry(rd_regions,
>  					struct vgic_redist_region, list);
> -		if (index != rdreg->index + 1)
> -			return -EINVAL;
>  
> -		/* Cannot add an explicitly sized regions after legacy region */
> -		if (!rdreg->count)
> +		if ((!count) != (!rdreg->count))
> +			return -EINVAL; /* Mix REDIST and REDIST_REGION */

Urgh... The triple negation killed me. Can we come up with a more
intuitive expression? Something like:

		/* Don't mix single region and discrete redist regions */
		if (!count && rdreg->count)
			return -EINVAL;

Does it capture what you want to express?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.