linux-kernel - Re: [PATCH v2 11/12] iommu/amd: Add support for nested domain attach/detach

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Message-ID: <20251006145900.GT3360665@nvidia.com>
Date: Mon, 6 Oct 2025 11:59:00 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc: nicolinc@...dia.com, linux-kernel@...r.kernel.org, robin.murphy@....com,
	will@...nel.org, joro@...tes.org, kevin.tian@...el.com,
	jsnitsel@...hat.com, vasant.hegde@....com, iommu@...ts.linux.dev,
	santosh.shukla@....com, sairaj.arunkodilkar@....com,
	jon.grimm@....com, prashanthpra@...gle.com, wvw@...gle.com,
	wnliu@...gle.com, gptran@...gle.com, kpsingh@...gle.com,
	joao.m.martins@...cle.com, alejandro.j.jimenez@...cle.com
Subject: Re: [PATCH v2 11/12] iommu/amd: Add support for nested domain
 attach/detach

On Wed, Oct 01, 2025 at 06:09:53AM +0000, Suravee Suthikulpanit wrote:
> +static void set_dte_nested(struct amd_iommu *iommu,
> +			   struct dev_table_entry *gdte,
> +			   struct nested_domain *ndom,
> +			   struct iommu_dev_data *dev_data)
> +{
> +	struct dev_table_entry *initial_dte;
> +	struct dev_table_entry new = {0};
> +	struct protection_domain *pdom = dev_data->parent;

No, this is ndom->parent.

The parent is NOT required to be attached to the device already.

> +	if (WARN_ON(!ndom || !pdom || (pdom->iop.mode == PAGE_MODE_NONE)))
> +		return;
> +
> +	amd_iommu_make_clear_dte(dev_data, &new);
> +
> +	new.data[0] |= iommu_virt_to_phys(pdom->iop.root);
> +	new.data[0] |= FIELD_PREP(DTE_MODE_MASK, pdom->iop.mode);
> +	new.data[0] |= DTE_FLAG_IR | DTE_FLAG_IW | DTE_FLAG_TV;
> +	new.data[0] |= (DTE_FLAG_PPR & gdte->data[0]);

> +	if (pdom->dirty_tracking)
> +		new.data[0] |= DTE_FLAG_HAD;
> +
> +	if (dev_data->ats_enabled)
> +		new.data[1] |= DTE_FLAG_IOTLB;

This sequence should be in some set_dte_gcr3() ??

> +	/*
> +	 * Restore cached persistent DTE bits, which can be set by information
> +	 * in IVRS table. See set_dev_entry_from_acpi().
> +	 */
> +	initial_dte = amd_iommu_get_ivhd_dte_flags(iommu->pci_seg->id, dev_data->devid);
> +	if (initial_dte) {
> +		new.data128[0] |= initial_dte->data128[0];
> +		new.data128[1] |= initial_dte->data128[1];
> +	}

This should go into amd_iommu_make_clear_dte() I think, and refactor
it out of iommu_update_dte256() ?

Every created DTE needs these bits set, right?

> +
> +	/* Guest translation stuff */
> +	new.data[0] |= (gdte->data[0] &
> +		       (DTE_GLX | DTE_FLAG_GV | DTE_FLAG_GIOV));
> +
> +	/* GCR3 table */
> +	new.data[0] |= (gdte->data[0] & DTE_GCR3_14_12);
> +	new.data[1] |= (gdte->data[1] & (DTE_GCR3_30_15 | DTE_GCR3_51_31));
> +
> +	/* Guest paging mode */
> +	new.data[2] |= (gdte->data[2] & DTE_GPT_LEVEL_MASK);

I didn't see anything validating gdte has only permitted set bits in
the prior patch?

If this is goint to decode array item by item then why not use struct
iommu_hwpt_amd_guest in the nested_domain ?

> +static int nested_attach_device(struct iommu_domain *dom, struct device *dev)
> +{
> +	struct iommu_dev_data *dev_data = dev_iommu_priv_get(dev);
> +	struct amd_iommu *iommu = get_amd_iommu_from_dev_data(dev_data);
> +	struct nested_domain *ndom = to_ndomain(dom);
> +	struct dev_table_entry *gdte = &ndom->guest_dte;
> +	int ret = 0;
> +
> +	if (dev_data->ndom == ndom)
> +		return ret;
> +
> +	if (!dev_is_pci(dev))
> +		return -EINVAL;

Why?

> +	/* Currently only support GCR3TRPMode with nested translation */
> +	if (!check_feature2(FEATURE_GCR3TRPMODE))
> +		return -EOPNOTSUPP;

This is impossible since we can't allocate a nest parent. If you want
to make a redundent check then call is_nest_parent_supported()

> +	/* We need to check host capability before setting the mode */
> +	if ((FIELD_GET(DTE_GPT_LEVEL_MASK, gdte->data[2]) == GUEST_PGTABLE_5_LEVEL) &&
> +	    (amd_iommu_gpt_level < PAGE_MODE_5_LEVEL))
> +		return -EOPNOTSUPP;

I wonder if this should be done during alloc

> +	WARN_ON(dev_data->ndom);
> +
> +	dev_data->ndom = ndom;

Useless?

> +	mutex_lock(&dev_data->mutex);
> +
> +	/* Update device table entry */
> +	set_dte_nested(iommu, gdte, ndom, dev_data);
> +	amd_iommu_device_flush_dte(dev_data);
> +	amd_iommu_completion_wait(iommu);

Hurray

Jason