linux-kernel - Re: [PATCH v13 6/6] iommu: Remove mode argument from iommu_set_dma

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Message-ID: <cac021f9-8469-a3b4-a0c6-80a37e882b6f@linux.intel.com>
Date:   Fri, 18 Jun 2021 09:52:29 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     John Garry <john.garry@...wei.com>, joro@...tes.org,
        will@...nel.org, dwmw2@...radead.org, robin.murphy@....com,
        corbet@....net
Cc:     baolu.lu@...ux.intel.com, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linuxarm@...wei.com,
        thunder.leizhen@...wei.com, chenxiang66@...ilicon.com,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v13 6/6] iommu: Remove mode argument from
 iommu_set_dma_strict()

On 6/17/21 3:41 PM, John Garry wrote:
> 
>>> @@ -349,10 +349,9 @@ static int __init iommu_dma_setup(char *str)
>>>   }
>>>   early_param("iommu.strict", iommu_dma_setup);
>>> -void iommu_set_dma_strict(bool strict)
>>> +void iommu_set_dma_strict(void)
>>>   {
>>> -    if (strict || !(iommu_cmd_line & IOMMU_CMD_LINE_STRICT))
>>> -        iommu_dma_strict = strict;
>>> +    iommu_dma_strict = true;
>>
>> Sorry, I still can't get how iommu.strict kernel option works.
>>
>> static int __init iommu_dma_setup(char *str)
>> {
>>          int ret = kstrtobool(str, &iommu_dma_strict);
>>
>>          if (!ret)
>>                  iommu_cmd_line |= IOMMU_CMD_LINE_STRICT;
>>          return ret;
>> }
>> early_param("iommu.strict", iommu_dma_setup);
>>
>> The bit IOMMU_CMD_LINE_STRICT is only set, but not used anywhere.
> 
> It is used in patch 2/6:
> 
> +    pr_info("DMA domain TLB invalidation policy: %s mode %s\n",
> +        iommu_dma_strict ? "strict" : "lazy",
> +        (iommu_cmd_line & IOMMU_CMD_LINE_STRICT) ?
> +            "(set via kernel command line)" : "");
> 
>> Hence,
>> I am wondering how could it work? A bug or I missed anything?
> 
> It is really just used for informative purpose now.

I am clear now. Thanks!

Best regards,
baolu