linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Enable PASID during iommu device probe

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Date:   Thu, 15 Sep 2022 15:21:18 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] iommu/vt-d: Enable PASID during iommu device probe

On 2022/9/15 11:22, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@...ux.intel.com>
>> Sent: Tuesday, September 13, 2022 5:25 PM
>>
>> On 2022/9/13 16:01, Tian, Kevin wrote:
>>>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>>>> Sent: Monday, September 12, 2022 10:48 AM
>>>>
>>>> @@ -1401,7 +1403,6 @@ static void iommu_enable_dev_iotlb(struct
>>>> device_domain_info *info)
>>>
>>> This is not the right name now as dev_iotlb is only related to ATS.
>>
>> Yes. This name is confusing. Perhaps we can split it into some specific
>> helpers,
>>
>> - intel_iommu_enable_pci_ats()
>> - intel_iommu_enabel_pci_pri()
>> - intel_iommu_enable_pci_pasid()
>> ?
> 
> Probably intel_iommu_enable_pci_caps()

It's better.

> 
>>
>>>
>>>>    		info->pfsid = pci_dev_id(pf_pdev);
>>>>    	}
>>>>
>>>> -#ifdef CONFIG_INTEL_IOMMU_SVM
>>>>    	/* The PCIe spec, in its wisdom, declares that the behaviour of
>>>>    	   the device if you enable PASID support after ATS support is
>>>>    	   undefined. So always enable PASID support on devices which
>>>> @@ -1414,7 +1415,7 @@ static void iommu_enable_dev_iotlb(struct
>>>> device_domain_info *info)
>>>>    	    (info->pasid_enabled ? pci_prg_resp_pasid_required(pdev) : 1)
>>>> &&
>>>>    	    !pci_reset_pri(pdev) && !pci_enable_pri(pdev, PRQ_DEPTH))
>>>>    		info->pri_enabled = 1;
>>>> -#endif
>>>> +
>>>>    	if (info->ats_supported && pci_ats_page_aligned(pdev) &&
>>>>    	    !pci_enable_ats(pdev, VTD_PAGE_SHIFT)) {
>>>>    		info->ats_enabled = 1;
>>>
>>> iommu_enable_dev_iotlb() is currently called both when the device is
>> probed
>>> and when sva is enabled (which is actually useless). From this angle the
>> commit
>>> msg is inaccurate.
>>
>> The logic is a bit tricky. iommu_support_dev_iotlb() only returns a
>> devinfo pointer when ATS is supported on the device. So, you are right
>> if device supports both ATS and PASID; otherwise PASID will not be
>> enabled.
> 
> Yes, that is what the first part of this patch fixes.
> 
> But my point is about the message that previously PASID was enabled
> only when FEAT_SVA is enabled and now the patch moves it to the
> probe time.
> 
> My point is that even in old way iommu_enable_dev_iotlb() was called
> twice: one at probe time and the other at FEAT_SVA. If ATS exists
> then PASID is enabled at probe time already. If ATS doesn't exist then
> PASID is always disabled.
> 
> So this patch is really to decouple PASID enabling from ATS and remove
> the unnecessary/duplicated call of iommu_enable_dev_iotlb() in
> intel_iommu_enable_sva().

Yes. Exactly. I will rephrase the commit message and send a v2.

Best regards,
baolu