linux-kernel - Re: [PATCH v3 7/7] dmaengine/idxd: Re-enable kernel workqueue under DMA API

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Message-ID: <07b7a01f-8a0d-6eca-e436-df5135d679cb@linux.intel.com>
Date:   Sat, 1 Apr 2023 21:39:32 +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,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Joerg Roedel <joro@...tes.org>, dmaengine@...r.kernel.org,
        vkoul@...nel.org
Cc:     baolu.lu@...ux.intel.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 v3 7/7] dmaengine/idxd: Re-enable kernel workqueue under
 DMA API

On 2023/4/1 7:11, Jacob Pan wrote:
>   static void idxd_disable_system_pasid(struct idxd_device *idxd)
>   {
> +	struct pci_dev *pdev = idxd->pdev;
> +	struct device *dev = &pdev->dev;
> +	struct iommu_domain *domain;
> +	union gencfg_reg gencfg;
> +
> +	domain = iommu_get_domain_for_dev(dev);
> +	if (!domain || domain->type == IOMMU_DOMAIN_BLOCKED)
> +		return;

Out of curiosity, why do you need to check the domain type? And, in
which case could the domain for the device be changed to a blocking one?

Once a driver is bound to the device, the driver "owns" the DMA of the
device. No one else could change the domain except the driver itself.

> +
> +	iommu_detach_device_pasid(domain, dev, idxd->pasid);
> +	iommu_free_global_pasid(idxd->pasid);
>   
> -	iommu_sva_unbind_device(idxd->sva);
> +	gencfg.bits = ioread32(idxd->reg_base + IDXD_GENCFG_OFFSET);
> +	gencfg.user_int_en = 0;
> +	iowrite32(gencfg.bits, idxd->reg_base + IDXD_GENCFG_OFFSET);
>   	idxd->sva = NULL;
> +	idxd->pasid = IOMMU_PASID_INVALID;
>   }

Best regards,
baolu