Re: [PATCH RFC 10/12] iommufd: Add kAPI toward external drivers

From: Jason Gunthorpe <jgg@nvidia.com>
To: Yi Liu <yi.l.liu@intel.com>
Cc: Alex Williamson <alex.williamson@redhat.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Chaitanya Kulkarni <chaitanyak@nvidia.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Daniel Jordan <daniel.m.jordan@oracle.com>,
	David Gibson <david@gibson.dropbear.id.au>,
	Eric Auger <eric.auger@redhat.com>,
	iommu@lists.linux-foundation.org,
	Jason Wang <jasowang@redhat.com>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Joao Martins <joao.m.martins@oracle.com>,
	Kevin Tian <kevin.tian@intel.com>,
	kvm@vger.kernel.org, Matthew Rosato <mjrosato@linux.ibm.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Nicolin Chen <nicolinc@nvidia.com>,
	Niklas Schnelle <schnelle@linux.ibm.com>,
	Shameerali Kolothum Thodi  <shameerali.kolothum.thodi@huawei.com>,
	Keqian Zhu <zhukeqian1@huawei.com>
Subject: Re: [PATCH RFC 10/12] iommufd: Add kAPI toward external drivers
Date: Thu, 19 May 2022 09:35:40 -0300	[thread overview]
Message-ID: <20220519123540.GY1343366@nvidia.com> (raw)
In-Reply-To: <5aab6dbf-df12-34f1-4135-857174fbe083@intel.com>

On Thu, May 19, 2022 at 05:45:06PM +0800, Yi Liu wrote:
> Hi Jason,
> 
> On 2022/3/19 01:27, Jason Gunthorpe wrote:
> 
> > +/**
> > + * iommufd_device_attach - Connect a device to an iommu_domain
> > + * @idev: device to attach
> > + * @pt_id: Input a IOMMUFD_OBJ_IOAS, or IOMMUFD_OBJ_HW_PAGETABLE
> > + *         Output the IOMMUFD_OBJ_HW_PAGETABLE ID
> > + * @flags: Optional flags
> > + *
> > + * This connects the device to an iommu_domain, either automatically or manually
> > + * selected. Once this completes the device could do DMA.
> > + *
> > + * The caller should return the resulting pt_id back to userspace.
> > + * This function is undone by calling iommufd_device_detach().
> > + */
> > +int iommufd_device_attach(struct iommufd_device *idev, u32 *pt_id,
> > +			  unsigned int flags)
> > +{

> Just double check here.
> This API doesn't prevent caller from calling this API multiple times with
> the same @idev and @pt_id. right? Note that idev has only one device_item
> list head. If caller does do multiple callings, then there should be
> problem. right? If so, this API assumes caller should take care of it and
> not do such bad function call. Is this the design here?

Yes, caller must ensure strict pairing, we don't have an assertion to
check it.

Jason