linux-kernel - Re: [PATCH v12 3/5] iommu/vt-d: Add support for IOMMU default DMA mode build options

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Message-ID: <0a04f964-80f4-7b2a-9740-eae4596e4e09@arm.com>
Date:   Mon, 14 Jun 2021 15:11:46 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     John Garry <john.garry@...wei.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>, joro@...tes.org,
        will@...nel.org, dwmw2@...radead.org
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linuxarm@...wei.com, thunder.leizhen@...wei.com,
        chenxiang66@...ilicon.com
Subject: Re: [PATCH v12 3/5] iommu/vt-d: Add support for IOMMU default DMA
 mode build options

On 2021-06-14 08:53, John Garry wrote:
> On 12/06/2021 03:22, Lu Baolu wrote:
>> On 2021/6/11 20:20, John Garry wrote:
>>> @@ -453,8 +452,7 @@ static int __init intel_iommu_setup(char *str)
>>>               pr_warn("intel_iommu=forcedac deprecated; use 
>>> iommu.forcedac instead\n");
>>>               iommu_dma_forcedac = true;
>>>           } else if (!strncmp(str, "strict", 6)) {
>>> -            pr_info("Disable batched IOTLB flush\n");
>>> -            intel_iommu_strict = 1;
>>> +            iommu_set_dma_strict(true);
>>
>> I would like to deprecate this command line and ask users to use
>> iommu.strict instead.
> 
> ok, but then I should probably make the AMD driver also officially 
> support this.

Oops, I should have documented that "iommu.strict" already applies to 
x86 as well. The interaction with the driver-specific parameters is a 
bit weird and unintuitive, but it was done knowingly. Let me quickly 
spin a kernel-parameters.txt fix for that...

Cheers,
Robin.

>>
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -436,7 +436,7 @@ static int __init intel_iommu_setup(char *str)
>>                          pr_warn("intel_iommu=forcedac deprecated; use 
>> iommu.forcedac instead\n");
>>                          iommu_dma_forcedac = true;
>>                  } else if (!strncmp(str, "strict", 6)) {
>> -                       pr_info("Disable batched IOTLB flush\n");
>> +                       pr_warn("intel_iommu=strict deprecated; use 
>> iommu.strict instead\n");
>>                          intel_iommu_strict = 1;
>>
>> Also update Documentation/admin-guide/kernel-parameters.txt accordingly.
> 
> Thanks,
> John