linux-kernel - Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

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Date:   Mon, 10 May 2021 15:28:54 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     "Raj, Ashok" <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        Auger Eric <eric.auger@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Jonathan Corbet <corbet@....net>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs

Hi Jason,

On Mon, 10 May 2021 13:39:56 -0300, Jason Gunthorpe <jgg@...dia.com> wrote:

> I still think it is smarter to push a group of RID's into a global
> allocation group and accept there are potential downsides with that
> than to try to force a global allocation group on every RID and then
> try to fix the mess that makes for non-ENQCMD devices.
The proposed ioasid_set change in this set has a token for each set of
IOASIDs.

/**
 * struct ioasid_set - Meta data about ioasid_set
 * @nh:		List of notifiers private to that set
 * @xa:		XArray to store ioasid_set private IDs, can be used for
 *		guest-host IOASID mapping, or just a private IOASID namespace.
 * @token:	Unique to identify an IOASID set
 * @type:	Token types
 * @quota:	Max number of IOASIDs can be allocated within the set
 * @nr_ioasids:	Number of IOASIDs currently allocated in the set
 * @id:		ID of the set
 */
struct ioasid_set {
	struct atomic_notifier_head nh;
	struct xarray xa;
	void *token;
	int type;
	int quota;
	atomic_t nr_ioasids;
	int id;
	struct rcu_head rcu;
	struct misc_cg *misc_cg; /* For misc cgroup accounting */
};

To satisfy your "give me a PASID for this RID" proposal, can we just use
the RID's struct device as the token? Also add a type field to explicitly
indicate global vs per-set(per-RID). i.e.

ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
		       int type, void *private)
Where flags can be:
enum ioasid_hwid_type {
	IOASID_HWID_GLOBAL,
	IOASID_HWID_PER_SET,
};

We are really talking about the HW IOASID, just a reminder.

Thanks,

Jacob