linux-kernel - Re: [PATCH v2 5/5] iommu/vt-d: Move PRI handling to IOPF feature path

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Date:   Fri, 17 Mar 2023 08:47:35 +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>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] iommu/vt-d: Move PRI handling to IOPF feature path

On 2023/3/17 8:06, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@...ux.intel.com>
>> Sent: Thursday, March 16, 2023 4:17 PM
>>
>> On 2023/3/16 15:17, Tian, Kevin wrote:
>>>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>>>> Sent: Thursday, March 9, 2023 10:57 AM
>>>>
>>>> @@ -4689,17 +4704,21 @@ static int intel_iommu_disable_iopf(struct
>> device
>>>> *dev)
>>>>    {
>>>>    	struct device_domain_info *info = dev_iommu_priv_get(dev);
>>>>    	struct intel_iommu *iommu = info->iommu;
>>>> -	int ret;
>>>>
>>>> -	ret = iommu_unregister_device_fault_handler(dev);
>>>> -	if (ret)
>>>> -		return ret;
>>>> +	if (!info->pri_enabled)
>>>> +		return -EINVAL;
>>>>
>>>> -	ret = iopf_queue_remove_device(iommu->iopf_queue, dev);
>>>> -	if (ret)
>>>> -		iommu_register_device_fault_handler(dev,
>>>> iommu_queue_iopf, dev);
>>>> +	pci_disable_pri(to_pci_dev(dev));
>>>> +	info->pri_enabled = 0;
>>>>
>>>> -	return ret;
>>>> +	/*
>>>> +	 * With pri_enabled checked, unregistering fault handler and
>>>> +	 * removing device from iopf queue should never fail.
>>>> +	 */
>>>> +	iommu_unregister_device_fault_handler(dev);
>>>> +	iopf_queue_remove_device(iommu->iopf_queue, dev);
>>>> +
>>>> +	return 0;
>>>>    }
>>>
>>> PCIe spec says that clearing the enable bit doesn't mean in-fly
>>> page requests are completed:
>>> --
>>> Enable (E) - This field, when set, indicates that the Page Request
>>> Interface is allowed to make page requests. If this field is Clear,
>>> the Page Request Interface is not allowed to issue page requests.
>>> If both this field and the Stopped field are Clear, then the Page
>>> Request Interface will not issue new page requests, but has
>>> outstanding page requests that have been transmitted or are
>>> queued for transmission
>>
>> Yes. So the iommu driver should drain the in-fly PRQs.
>>
>> The Intel VT-d implementation drains the PRQs when any PASID is unbound
>> from the iommu domain (see intel_svm_drain_prq()) before reuse. Before
>> disabling iopf, the device driver should unbind pasid and disable sva,
>> so when it comes here, the PRQ should have been drained.
>>
>> Perhaps I can add below comments to make this clear:
>>
>>           /*
>>            * PCIe spec states that by clearing PRI enable bit, the Page
>>            * Request Interface will not issue new page requests, but has
>>            * outstanding page requests that have been transmitted or are
>>            * queued for transmission. This is supposed to be called after
>>            * the device driver has stopped DMA, all PASIDs have been
>>            * unbound and the outstanding PRQs have been drained.
>>            */
>>
> 
> this is fine. But it should be a separate patch which removes
> check of return value. It's not caused by this PRI handling move
> patch.

Okay, that will be clearer.

Best regards,
baolu