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Date:   Fri, 29 Jul 2022 11:20:49 +0800
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Cc:     baolu.lu@linux.intel.com, Joerg Roedel <joro@8bytes.org>,
        Christoph Hellwig <hch@infradead.org>,
        "Raj, Ashok" <ashok.raj@intel.com>, Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        "Jiang, Dave" <dave.jiang@intel.com>,
        Vinod Koul <vkoul@kernel.org>,
        Eric Auger <eric.auger@redhat.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        "Pan, Jacob jun" <jacob.jun.pan@intel.com>,
        Zhangfei Gao <zhangfei.gao@linaro.org>,
        "Zhu, Tony" <tony.zhu@intel.com>,
        "iommu@lists.linux.dev" <iommu@lists.linux.dev>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>
Subject: Re: [PATCH v10 04/12] iommu: Add attach/detach_dev_pasid iommu
 interface
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To:     "Tian, Kevin" <kevin.tian@intel.com>,
        Jason Gunthorpe <jgg@nvidia.com>
References: <20220705050710.2887204-1-baolu.lu@linux.intel.com>
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From:   Baolu Lu <baolu.lu@linux.intel.com>
In-Reply-To: <BN9PR11MB52761058CFCB9397F6A73A958C999@BN9PR11MB5276.namprd11.prod.outlook.com>
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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