linux-kernel - Re: [PATCH 2/2] iommu/vt-d: Move iopf code from SVA to IOPF enabling path

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Date:   Tue, 7 Feb 2023 14:30:46 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] iommu/vt-d: Move iopf code from SVA to IOPF enabling
 path

On 2023/2/6 11:28, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>> Sent: Friday, February 3, 2023 4:45 PM
>>
>> Generally enabling IOMMU_DEV_FEAT_SVA requires
>> IOMMU_DEV_FEAT_IOPF, but
>> some devices manage I/O Page Faults themselves instead of relying on the
>> IOMMU. Move IOPF related code from SVA to IOPF enabling path to make
>> the
>> driver work for devices that manage IOPF themselves.
>>
>> For the device drivers that relies on the IOMMU for IOPF through PCI/PRI,
>> IOMMU_DEV_FEAT_IOPF must be enabled before and disabled after
>> IOMMU_DEV_FEAT_SVA.
> 
> ARM still handles this differently:
> 
> arm_smmu_master_enable_sva()
>    arm_smmu_master_sva_enable_iopf():
> {
> 	/*
> 	 * Drivers for devices supporting PRI or stall should enable IOPF first.
> 	 * Others have device-specific fault handlers and don't need IOPF.
> 	 */
> 	if (!arm_smmu_master_iopf_supported(master))
> 		return 0;
> 
> 	if (!master->iopf_enabled)
> 		return -EINVAL;
> }
> 
> i.e. device specific IOPF is allowed only when PRI or stall is not supported.
> 
> it's different from what this patch does to allow device specific IOPF even
> when PRI is supported.
> 
> should we make them consistent given SVA/IOPF capabilities are general
> iommu definitions or fine to leave each iommu driver with different
> restriction?

Good point! I prefer the former. I will add a check in sva enabling path
and return failure if device supports PRI but not enabled (that
implies device has its specific IOPF handling).

> 
>>
>> -	ret = iopf_queue_add_device(iommu->iopf_queue, dev);
>> -	if (!ret)
>> -		ret = iommu_register_device_fault_handler(dev,
>> iommu_queue_iopf, dev);
>> -
>> -	return ret;
>> +	return 0;
>>   }
> 
> here and below...
> 
>> +	ret = iopf_queue_add_device(info->iommu->iopf_queue, dev);
>> +	if (ret)
>> +		return ret;
>> +
>> +	ret = iommu_register_device_fault_handler(dev, iommu_queue_iopf,
>> dev);
>> +	if (ret)
>> +		iopf_queue_remove_device(info->iommu->iopf_queue, dev);
>> +
>> +	return ret;
>>   }
> 
> ...indicate a bug fix on error handling. better to have the fix as
> a separate patch and then move code.
> 

Yes. I will post a fix patch before this move.

Best regards,
baolu