linux-kernel - Re: [PATCH 11/17] iommu/vt-d: Fix operand size in bitwise operation

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Date:   Wed, 12 Apr 2023 21:10:30 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     David Laight <David.Laight@...LAB.COM>,
        Joerg Roedel <joro@...tes.org>
Cc:     baolu.lu@...ux.intel.com, Vinod Koul <vkoul@...nel.org>,
        Tina Zhang <tina.zhang@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/17] iommu/vt-d: Fix operand size in bitwise operation

On 2023/4/12 15:11, David Laight wrote:
> From: Baolu Lu
>> Sent: 12 April 2023 02:32
>>
>> On 4/12/23 5:22 AM, David Laight wrote:
>>>> Sent: 11 April 2023 07:48
>>>>
>>>> From: Tina Zhang<tina.zhang@...el.com>
>>>>
>>>> The patch fixes the klocwork issues that operands in a bitwise operation
>>>> have different size at line 1692 of dmar.c, line 1898 and line 1907 of
>>>> iommu.c.
>>> Why is this any kind of thing that needs fixing?
>>
>> This description is a bit misleading. Actually I queued it as a cleanup
>> patch.
> 
> Hopefully without 'fix' anywhere in the description.
> Otherwise the scripts will pick it for a back-port.

Fair enough.I will refine the commit message like below:

iommu/vt-d: Make size of operands same in bitwise operations

The addresses the following issue reported by klocwork tool:

  - operands of different size in bitwise operations

Suggested-by: Yongwei Ma <yongwei.ma@...el.com>
Signed-off-by: Tina Zhang <tina.zhang@...el.com>

> 
>>> -		val |= (1 << 11) | 1;
>>> +		val |= BIT_ULL(11) | BIT_ULL(0);
> 
> More problematic it what is bit 11 anyway?

There is already a comment at the top of the code explaining the meaning
of these bits. Because this is not a newly added code, it is not
displayed in this patch.

         /*
          * Set DW=1 and QS=1 in IQA_REG when Scalable Mode capability
          * is present.
          */
         if (ecap_smts(iommu->ecap))
                 val |= BIT_ULL(11) | BIT_ULL(0);

Best regards,
baolu