linux-kernel - RE: [PATCH 4/4] dmaengine/idxd: Re-enable kernel workqueue under DMA API

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Date:   Thu, 2 Mar 2023 09:47:00 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Jason Gunthorpe <jgg@...dia.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>
CC:     Robin Murphy <robin.murphy@....com>, Will Deacon <will@...nel.org>,
        "David Woodhouse" <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>
Subject: RE: [PATCH 4/4] dmaengine/idxd: Re-enable kernel workqueue under DMA
 API

> From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Sent: Thursday, March 2, 2023 9:00 AM
> 
>  static int idxd_enable_system_pasid(struct idxd_device *idxd)
>  {
> -	return -EOPNOTSUPP;
> +	struct pci_dev *pdev = idxd->pdev;
> +	struct device *dev = &pdev->dev;
> +	struct iommu_domain *domain;
> +	union gencfg_reg gencfg;
> +	ioasid_t pasid;
> +	int ret;
> +
> +	domain = iommu_get_domain_for_dev(dev);
> +	if (!domain || domain->type == IOMMU_DOMAIN_BLOCKED)
> +		return -EPERM;

what about UNMANAGED?

> +
> +	pasid = iommu_sva_reserve_pasid(1, dev->iommu->max_pasids);
> +	if (pasid == IOMMU_PASID_INVALID)
> +		return -ENOSPC;

as commented in last patch we can just pass a device pointer to a
general allocation interface.

> +
> +	ret = iommu_attach_device_pasid(domain, dev, pasid);
> +	if (ret) {
> +		dev_err(dev, "failed to attach device pasid %d, domain
> type %d",
> +			pasid, domain->type);
> +		iommu_sva_unreserve_pasid(pasid);
> +		return ret;
> +	}
> +
> +	/* Since we set user privilege for kernel DMA, enable completion IRQ
> */
> +	gencfg.bits = ioread32(idxd->reg_base + IDXD_GENCFG_OFFSET);
> +	gencfg.user_int_en = 1;
> +	iowrite32(gencfg.bits, idxd->reg_base + IDXD_GENCFG_OFFSET);
> +	idxd->pasid = pasid;

Why does user privilege requires a completion interrupt?

Or instead it's more due to doing kernel DMA itself then we certainly
don't want to poll in the kernel?