linux-kernel - Re: [PATCH v8 02/10] iommu/vt-d: Add nested translation helper function

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Date:   Wed, 18 Dec 2019 10:41:53 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>
Cc:     baolu.lu@...ux.intel.com, "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        Eric Auger <eric.auger@...hat.com>,
        Yi L <yi.l.liu@...ux.intel.com>
Subject: Re: [PATCH v8 02/10] iommu/vt-d: Add nested translation helper
 function

Hi again,

On 12/17/19 3:24 AM, Jacob Pan wrote:
> +/**
> + * intel_pasid_setup_nested() - Set up PASID entry for nested translation
> + * which is used for vSVA. The first level page tables are used for
> + * GVA-GPA or GIOVA-GPA translation in the guest, second level page tables
> + *  are used for GPA-HPA translation.
> + *
> + * @iommu:      Iommu which the device belong to
> + * @dev:        Device to be set up for translation
> + * @gpgd:       FLPTPTR: First Level Page translation pointer in GPA
> + * @pasid:      PASID to be programmed in the device PASID table
> + * @pasid_data: Additional PASID info from the guest bind request
> + * @domain:     Domain info for setting up second level page tables
> + * @addr_width: Address width of the first level (guest)
> + */
> +int intel_pasid_setup_nested(struct intel_iommu *iommu,
> +			struct device *dev, pgd_t *gpgd,
> +			int pasid, struct iommu_gpasid_bind_data_vtd *pasid_data,
> +			struct dmar_domain *domain,
> +			int addr_width)
> +{
> +	struct pasid_entry *pte;
> +	struct dma_pte *pgd;
> +	u64 pgd_val;
> +	int agaw;
> +	u16 did;
> +
> +	if (!ecap_nest(iommu->ecap)) {
> +		pr_err("IOMMU: %s: No nested translation support\n",
> +		       iommu->name);
> +		return -EINVAL;
> +	}
> +
> +	pte = intel_pasid_get_entry(dev, pasid);
> +	if (WARN_ON(!pte))
> +		return -EINVAL;
> +
> +	pasid_clear_entry(pte);

In some cases, e.g. nested mode for GIOVA-HPA, the PASID entry might
have already been setup for second level translation. (This could be
checked with the Present bit.) Hence, it's safe to flush caches here.

Or, maybe intel_pasid_tear_down_entry() is more suitable?

Best regards,
baolu