linux-kernel - Re: [PATCH v2 03/16] iommu: introduce iommu invalidate API function

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Date:   Tue, 10 Oct 2017 15:35:42 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        Lan Tianyu <tianyu.lan@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...ux.intel.com>, Liu@...tes.org
Subject: Re: [PATCH v2 03/16] iommu: introduce iommu invalidate API function

On Thu, Oct 05, 2017 at 04:03:31PM -0700, Jacob Pan wrote:
> +int iommu_invalidate(struct iommu_domain *domain,
> +		struct device *dev, struct tlb_invalidate_info *inv_info)

This name is way too generic, it should at least be called
iommu_svm_invalidate() or something like that. With the name above it is
easily confused with the other TLB invalidation functions of the
IOMMU-API.

> +enum iommu_inv_granularity {
> +	IOMMU_INV_GRANU_GLOBAL,		/* all TLBs invalidated */

Is that needed? We certainly don't want to give userspace/guests that
fine-grained control about IOMMU cache invalidations.

In the end a guest issues flush-global command does not translate to a
flush-global on the host, but to separate flushes for the domains the
guest uses.

> +	IOMMU_INV_GRANU_DOMAIN,		/* all TLBs associated with a domain */
> +	IOMMU_INV_GRANU_DEVICE,		/* caching structure associated with a
> +					 * device ID

What is the difference between a DOMAIN and a DEVICE flush?

> +	IOMMU_INV_GRANU_DOMAN_PAGE,	/* address range with a domain */
> +	IOMMU_INV_GRANU_ALL_PASID,	/* cache of a given PASID */
> +	IOMMU_INV_GRANU_PASID_SEL,	/* only invalidate specified PASID */
> +
> +	IOMMU_INV_GRANU_NG_ALL_PASID,	/* non-global within all PASIDs */
> +	IOMMU_INV_GRANU_NG_PASID,	/* non-global within a PASIDs */
> +	IOMMU_INV_GRANU_PAGE_PASID,	/* page-selective within a PASID */
> +	IOMMU_INV_NR_GRANU,
> +};
> +
> +enum iommu_inv_type {
> +	IOMMU_INV_TYPE_DTLB,	/* device IOTLB */
> +	IOMMU_INV_TYPE_TLB,	/* IOMMU paging structure cache */
> +	IOMMU_INV_TYPE_PASID,	/* PASID cache */
> +	IOMMU_INV_TYPE_CONTEXT,	/* device context entry cache */

Is that really needed? When the guest updates it context-entry
equivalent it translates to bind_pasid_table/unbind_pasid_table calls,
no?