linux-kernel - Re: [PATCH v2 5/8] iommu/vt-d: Make device pasid attachment explicit

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Date:   Tue, 28 Mar 2023 13:49:24 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
        Jason Gunthorpe <jgg@...dia.com>,
        Joerg Roedel <joro@...tes.org>, dmaengine@...r.kernel.org,
        vkoul@...nel.org
Cc:     baolu.lu@...ux.intel.com, Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>
Subject: Re: [PATCH v2 5/8] iommu/vt-d: Make device pasid attachment explicit

On 3/28/23 7:21 AM, Jacob Pan wrote:
> diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
> index 65b15be72878..b6c26f25d1ba 100644
> --- a/drivers/iommu/intel/iommu.h
> +++ b/drivers/iommu/intel/iommu.h
> @@ -595,6 +595,7 @@ struct dmar_domain {
>   
>   	spinlock_t lock;		/* Protect device tracking lists */
>   	struct list_head devices;	/* all devices' list */
> +	struct list_head dev_pasids;	/* all attached pasids */
>   
>   	struct dma_pte	*pgd;		/* virtual address */
>   	int		gaw;		/* max guest address width */
> @@ -708,6 +709,7 @@ struct device_domain_info {
>   	u8 ats_supported:1;
>   	u8 ats_enabled:1;
>   	u8 dtlb_extra_inval:1;	/* Quirk for devices need extra flush */
> +	u8 dev_attached:1;	/* Device context activated */
>   	u8 ats_qdep;
>   	struct device *dev; /* it's NULL for PCIe-to-PCI bridge */
>   	struct intel_iommu *iommu; /* IOMMU used by this device */
> @@ -715,6 +717,12 @@ struct device_domain_info {
>   	struct pasid_table *pasid_table; /* pasid table */
>   };
>   
> +struct device_pasid_info {
> +	struct list_head link_domain;	/* link to domain siblings */
> +	struct device *dev;		/* physical device derived from */
> +	ioasid_t pasid;			/* PASID on physical device */
> +};

The dev_pasids list seems to be duplicate with iommu_group::pasid_array.

The pasid_array is de facto per-device as the PCI subsystem requires ACS
to be enabled on the upstream path to the root port.

pci_enable_pasid():
385         if (!pci_acs_path_enabled(pdev, NULL, PCI_ACS_RR | PCI_ACS_UF))
386                 return -EINVAL;

For such PCI topology, pci_device_group() always assigns an exclusive
iommu group (a.k.a. singleton group).

So, how about moving the pasid_array from struct iommu_group to struct
dev_iommu? With this refactoring, the individual iommu driver has no
need to create their own pasid array or list.

Instead of using iommu_group::mutex, perhaps the pasid_array needs its
own lock in struct dev_iommu after moving.

Best regards,
baolu