linux-kernel - Re: [RFC] /dev/ioasid uAPI proposal

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Message-ID: <20210615230215.GA1002214@nvidia.com>
Date:   Tue, 15 Jun 2021 20:02:15 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "Alex Williamson (alex.williamson@...hat.com)" 
        <alex.williamson@...hat.com>, "Raj, Ashok" <ashok.raj@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Robin Murphy <robin.murphy@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        David Gibson <david@...son.dropbear.id.au>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Jason Wang <jasowang@...hat.com>
Subject: Re: [RFC] /dev/ioasid uAPI proposal

On Tue, Jun 15, 2021 at 10:59:06PM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@...dia.com>
> > Sent: Tuesday, June 15, 2021 11:07 PM
> > 
> > On Tue, Jun 15, 2021 at 08:59:25AM +0000, Tian, Kevin wrote:
> > > Hi, Jason,
> > >
> > > > From: Jason Gunthorpe
> > > > Sent: Thursday, June 3, 2021 9:05 PM
> > > >
> > > > On Thu, Jun 03, 2021 at 06:39:30AM +0000, Tian, Kevin wrote:
> > > > > > > Two helper functions are provided to support VFIO_ATTACH_IOASID:
> > > > > > >
> > > > > > > 	struct attach_info {
> > > > > > > 		u32	ioasid;
> > > > > > > 		// If valid, the PASID to be used physically
> > > > > > > 		u32	pasid;
> > > > > > > 	};
> > > > > > > 	int ioasid_device_attach(struct ioasid_dev *dev,
> > > > > > > 		struct attach_info info);
> > > > > > > 	int ioasid_device_detach(struct ioasid_dev *dev, u32 ioasid);
> > > > > >
> > > > > > Honestly, I still prefer this to be highly explicit as this is where
> > > > > > all device driver authors get invovled:
> > > > > >
> > > > > > ioasid_pci_device_attach(struct pci_device *pdev, struct ioasid_dev
> > *dev,
> > > > > > u32 ioasid);
> > > > > > ioasid_pci_device_pasid_attach(struct pci_device *pdev, u32
> > > > *physical_pasid,
> > > > > > struct ioasid_dev *dev, u32 ioasid);
> > > > >
> > > > > Then better naming it as pci_device_attach_ioasid since the 1st
> > parameter
> > > > > is struct pci_device?
> > > >
> > > > No, the leading tag indicates the API's primary subystem, in this case
> > > > it is iommu (and if you prefer list the iommu related arguments first)
> > > >
> > >
> > > I have a question on this suggestion when working on v2.
> > >
> > > Within IOMMU fd it uses only the generic struct device pointer, which
> > > is already saved in struct ioasid_dev at device bind time:
> > >
> > > 	struct ioasid_dev *ioasid_register_device(struct ioasid_ctx *ctx,
> > > 		struct device *device, u64 device_label);
> > >
> > > What does this additional struct pci_device bring when it's specified in
> > > the attach call? If we save it in attach_data, at which point will it be
> > > used or checked?
> > 
> > The above was for attaching to an ioasid not the register path
> 
> Yes, I know. and this is my question. When receiving a struct pci_device
> at attach time, what should IOMMU fd do with it? Just verify whether 
> pci_device->device is same as ioasid_dev->device? if saving it to per-device
> attach data under ioasid then when will it be further used?
> 
> I feel once ioasid_dev is returned in the register path, following operations
> (unregister, attach, detach) just uses ioasid_dev as the main object.

The point of having the pci_device specific API was to convey bus
specific information during the attachment to the IOASID.

The registration of the device to the iommu_fd doesn't need bus
specific information, AFIAK? So just use a normal struct device
pointer

Jason