linux-kernel - Re: [PATCH] scsi: mvumi: fix 32 bit shift of a u32 value

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Message-ID: <5D53B57B.3000905@bfs.de>
Date:   Wed, 14 Aug 2019 09:17:15 +0200
From:   walter harms <wharms@....de>
To:     Colin King <colin.king@...onical.com>
CC:     Jianyun Li <jyli@...vell.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: mvumi: fix 32 bit shift of a u32 value



Am 13.08.2019 20:01, schrieb Colin King:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently the top 32 bits of a 64 bit address is being calculated
> by shifting a u32 twice by 16 bits and then being cast into a 64
> bit address.  Shifting a u32 twice by 16 bits always ends up with
> a zero.  Fix this by casting the u32 to a 64 bit address first
> and then shifting it 32 bits.
> 
> Addresses-Coverity: ("Operands don't affect result")
> Fixes: f0c568a478f0 ("[SCSI] mvumi: Add Marvell UMI driver")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/scsi/mvumi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/mvumi.c b/drivers/scsi/mvumi.c
> index 8906aceda4c4..62df69f1e71e 100644
> --- a/drivers/scsi/mvumi.c
> +++ b/drivers/scsi/mvumi.c
> @@ -296,7 +296,7 @@ static void mvumi_delete_internal_cmd(struct mvumi_hba *mhba,
>  			sgd_getsz(mhba, m_sg, size);
>  
>  			phy_addr = (dma_addr_t) m_sg->baseaddr_l |
> -				(dma_addr_t) ((m_sg->baseaddr_h << 16) << 16);
> +				   (dma_addr_t) m_sg->baseaddr_h << 32;
>  

All the casts make it hard to read, i would propose an alternativ version:
phy_addr = m_sg->baseaddr_h;
phy_addr <<= 32;
phy_addr |= m_sg->baseaddr_l;

JM2C and totaly untested.

re,
 wh

>  			dma_free_coherent(&mhba->pdev->dev, size, cmd->data_buf,
>  								phy_addr);