linux-kernel - Re: [PATCH v10 04/12] iommu: Add attach/detach_dev

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Date:   Fri, 29 Jul 2022 11:20:49 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        "Zhu, Tony" <tony.zhu@...el.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH v10 04/12] iommu: Add attach/detach_dev_pasid iommu
 interface

On 2022/7/29 10:56, Tian, Kevin wrote:
>> +static bool iommu_group_device_pasid_viable(struct iommu_group *group,
>> +					    struct device *dev)
>> +{
>> +	int count;
>> +
>> +	count = iommu_group_device_count(group);
>> +	if (count != 1)
>> +		return false;
>> +
>> +	/*
>> +	 * Block PASID attachment in cases where the PCI fabric is
>> +	 * routing based on address. PCI/ACS disables that.
>> +	 */
>> +	if (dev_is_pci(dev))
>> +		return pci_acs_path_enabled(to_pci_dev(dev), NULL,
>> +					    REQ_ACS_FLAGS);
> I think we are leaning toward doing above check in pci_enable_pasid().
> Then no singleton check inside iommu core.

The iommu grouping also considers other things, like PCI alias. There
are many calls of pci_add_dma_alias() in drivers/pci/quirks.c.
Therefore, I believe that pci_acs_path_enabled() returning true doesn't
guarantees a singleton group.

> 
> Presumably similar check can be done in DT/ACPI path of enabling pasid?
> 

I can't find the pasid (or anything similar) enabling interfaces for
DT or ACPI. They are device specific?

Best regards,
baolu