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

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Date:   Tue, 13 Sep 2022 17:30:40 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Ethan Zhao <haifeng.zhao@...ux.intel.com>, 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>,
        Kevin Tian <kevin.tian@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/vt-d: Enable PASID during iommu device probe

Hi Ethan,

On 2022/9/13 15:46, Ethan Zhao wrote:
> Baolu,
> 
> 在 2022/9/12 10:48, Lu Baolu 写道:
>> Previously PASID supports on both IOMMU and PCI devices are enabled in 
>> the
>> iommu_dev_enable_feature(dev, IOMMU_DEV_FEAT_SVA) path. It's functionally
>> correct as the SVA is the only feature that requires PASID setup. 
>> However,
>> looking ahead, we will add more features that need to enable pasid (for
>> example, kernel DMA with PASID, SIOV, VM guest SVA, etc.). It makes more
>> sense to enable PASID during iommu probing device.
>>
>> This enables PASID during iommu probing device and deprecates the
>> intel_iommu_enable_pasid() helper. This is safe because the IOMMU 
>> hardware
>> will block any PCI TLP with a PASID prefix if there is no IOMMU domain
>> attached to the PASID of the device.
> 
> What the error path would be if this code runs on some old platforms don't
> 
> support PASID, would you print out "this platform doesn't suppor PASID" and
> 
> give users an interface function to query if the PASID cap of iommu is 
> enabled
> 
> and if not why ?

It's not an error case if the IOMMU doesn't support PASID. But it's an
error case if any device drivers call PASID related IOMMU interfaces
(for example, iommu_domain_attach/detach_dev_pasid()). The corresponding
error code will be returned to the drivers.

Best regards,
baolu