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

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Message-ID: <20210615150630.GS1002214@nvidia.com>
Date:   Tue, 15 Jun 2021 12:06:30 -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 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

You should call 'device_label' 'device_cookie' if it is a user
provided u64

Jason