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

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Message-ID: <826a10fa-7dc3-887d-8a08-e03dcf1fa59c@linux.intel.com>
Date:   Tue, 13 Sep 2022 17:25:00 +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 2022/9/13 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()
?

> 
>>   		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.

> 
>> diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
>> index 39a06d245f12..b3f40375f214 100644
>> --- a/drivers/iommu/intel/Kconfig
>> +++ b/drivers/iommu/intel/Kconfig
>> @@ -21,6 +21,8 @@ config INTEL_IOMMU
>>   	select IOASID
>>   	select IOMMU_DMA
>>   	select PCI_ATS
>> +	select PCI_PRI
>> +	select PCI_PASID
>>   	help
>>   	  DMA remapping (DMAR) devices support enables independent
>> address
>>   	  translations for Direct Memory Access (DMA) from devices.
>> @@ -48,8 +50,6 @@ config INTEL_IOMMU_DEBUGFS
>>   config INTEL_IOMMU_SVM
>>   	bool "Support for Shared Virtual Memory with Intel IOMMU"
>>   	depends on X86_64
>> -	select PCI_PASID
>> -	select PCI_PRI
>>   	select MMU_NOTIFIER
>>   	select IOASID
> 
> this is already selected by CONFIG_INTEL_IOMMU

Yes. Should be removed.

> 
>>   	select IOMMU_SVA
>> --
>> 2.25.1
> 
> 

Best regards,
baolu