linux-kernel - Re: [PATCH v3 15/16] iommu: introduce page response function

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Date:   Fri, 8 Dec 2017 12:40:17 -0800
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jean-Philippe Brucker <jean-philippe.brucker@....com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Lan Tianyu <tianyu.lan@...el.com>,
        Jean Delvare <khali@...ux-fr.org>,
        Will Deacon <Will.Deacon@....com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v3 15/16] iommu: introduce page response function

On Fri, 8 Dec 2017 13:52:00 +0000
Jean-Philippe Brucker <jean-philippe.brucker@....com> wrote:

> On 07/12/17 21:51, Alex Williamson wrote:
> >> Agree, IOMMU driver cannot enforce it. I think VFIO layer can make
> >> sure page response come from the assigned device and its
> >> guest/container.  
> > 
> > Can we enforce it via the IOMMU/VFIO interface?  If the response is
> > for a struct device, and not an rid/did embedded in a structure,
> > then vfio can pass it through w/o worrying about it, ie. response
> > comes in via ioctl with association to vfio device fd -> struct
> > vfio_device -> struct device, iommu driver fills in rid/did.
> > Thanks,  
> 
> Yes that's probably the best way, reporting faults and receiving
> responses on the device fd.
> 
Just to put these ideas in to code. The IOMMU API used by VFIO has
struct device* (derived from fd), no did/rid (to be derived from
struct device by IOMMU driver.)

int intel_iommu_page_response(struct iommu_domain *domain, struct device *dev,
			struct page_response_msg *msg)

IOMMU driver can further sanitize by checking whether this is a pending
page request for the device, and refcount outstanding PRQs.

Does it sound right?

/**
 * Generic page response information based on PCI ATS and PASID spec.
 * @addr: servicing page address
 * @pasid: contains process address space ID, used in shared virtual
memory(SVM)
 * @resp_code: response code
 * @page_req_group_id: page request group index
 * @type: group or stream/single page response
 * @private_data: uniquely identify device-specific private data for an
 *                individual page response

 */
struct page_response_msg {
	u64 addr;
	u32 pasid;
	u32 resp_code:4;
#define IOMMU_PAGE_RESP_SUCCESS	0
#define IOMMU_PAGE_RESP_INVALID	1
#define IOMMU_PAGE_RESP_FAILURE	0xF

	u32 pasid_present:1;
	u32 page_req_group_id : 9;
	enum page_response_type type;
	u32 private_data;
};