linux-kernel - Re: [PATCH] iommu/mediatek: Remove a unnecessary checking for larbid

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Message-ID: <633be7a7-0bb8-1575-535e-2f96302198bd@collabora.com>
Date:   Tue, 4 Jul 2023 14:19:39 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Yong Wu <yong.wu@...iatek.com>, Joerg Roedel <joro@...tes.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux.dev, linux-mediatek@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] iommu/mediatek: Remove a unnecessary checking for larbid

Il 04/07/23 13:56, Yong Wu ha scritto:
> Fix a coverity issue:
> 
>>> assignment: Assigning: larbid = (fwspec->ids[0] >> 5) & 0x1fU.
> 	larbid = MTK_M4U_TO_LARB(fwspec->ids[0]);
>>> between: At condition larbid >= 32U, the value of larbid must be between
>>> 0 and 31.
>>> dead_error_condition: The condition larbid >= 32U cannot be true.
> 	if (larbid >= MTK_LARB_NR_MAX)
>>> CID 11306470 (#1 of 1): Logically dead code (DEADCODE)
>>> dead_error_line: Execution cannot reach this statement:
>>> return ERR_PTR(-22L);
>          	return ERR_PTR(-EINVAL);
> 
> The checking "if (larbid >= MTK_LARB_NR_MAX)" is unnecessary.
> 

I agree with the coverity tool in that after the transformation (going through
the definition of MTK_M4U_TO_LARB) the check is pointless, but I think that the
right fix here is to check for validity of fwspec->ids[0] instead of simply
removing validation.

Having no validation after mtk_iommu_probe_device() is fine, but that's
because we assume that *this* function performs all validation steps.

Regards,
Angelo

> Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> ---
> Rebase on v6.4-rc1.
> ---
>   drivers/iommu/mtk_iommu.c | 3 ---
>   1 file changed, 3 deletions(-)
> 
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index aecc7d154f28..67caa90b481b 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -838,9 +838,6 @@ static struct iommu_device *mtk_iommu_probe_device(struct device *dev)
>   	 * All the ports in each a device should be in the same larbs.
>   	 */
>   	larbid = MTK_M4U_TO_LARB(fwspec->ids[0]);
> -	if (larbid >= MTK_LARB_NR_MAX)
> -		return ERR_PTR(-EINVAL);
> -
>   	for (i = 1; i < fwspec->num_ids; i++) {
>   		larbidx = MTK_M4U_TO_LARB(fwspec->ids[i]);
>   		if (larbid != larbidx) {