RE: [PATCH v5 10/19] iommufd: Data structure to provide IOVA to PFN mapping

From: "Tian, Kevin" <kevin.tian@intel.com>
To: Jason Gunthorpe <jgg@nvidia.com>,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,
	David Woodhouse <dwmw2@infradead.org>,
	"iommu@lists.linux.dev" <iommu@lists.linux.dev>,
	Joerg Roedel <joro@8bytes.org>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"linux-kselftest@vger.kernel.org"
	<linux-kselftest@vger.kernel.org>,
	"llvm@lists.linux.dev" <llvm@lists.linux.dev>,
	Nathan Chancellor <nathan@kernel.org>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	Miguel Ojeda <ojeda@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Shuah Khan <shuah@kernel.org>,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	Tom Rix <trix@redhat.com>, Will Deacon <will@kernel.org>
Cc: Anthony Krowiak <akrowiak@linux.ibm.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	Bagas Sanjaya <bagasdotme@gmail.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>,
	Eric Farman <farman@linux.ibm.com>,
	Jason Wang <jasowang@redhat.com>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Jason Herne <jjherne@linux.ibm.com>,
	"Martins, Joao" <joao.m.martins@oracle.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"Yang, Lixiao" <lixiao.yang@intel.com>,
	Matthew Rosato <mjrosato@linux.ibm.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Nicolin Chen <nicolinc@nvidia.com>,
	Halil Pasic <pasic@linux.ibm.com>,
	Niklas Schnelle <schnelle@linux.ibm.com>,
	Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
	"Liu, Yi L" <yi.l.liu@intel.com>,
	Keqian Zhu <zhukeqian1@huawei.com>
Subject: RE: [PATCH v5 10/19] iommufd: Data structure to provide IOVA to PFN mapping
Date: Fri, 18 Nov 2022 02:55:20 +0000	[thread overview]
Message-ID: <BN9PR11MB52761E296D2EC7A8174D2E998C099@BN9PR11MB5276.namprd11.prod.outlook.com> (raw)
In-Reply-To: <10-v5-4001c2997bd0+30c-iommufd_jgg@nvidia.com>

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Thursday, November 17, 2022 5:01 AM
> 
> This is the remainder of the IOAS data structure. Provide an object called
> an io_pagetable that is composed of iopt_areas pointing at iopt_pages,
> along with a list of iommu_domains that mirror the IOVA to PFN map.
> 
> At the top this is a simple interval tree of iopt_areas indicating the map
> of IOVA to iopt_pages. An xarray keeps track of a list of domains. Based
> on the attached domains there is a minimum alignment for areas (which may
> be smaller than PAGE_SIZE), an interval tree of reserved IOVA that can't
> be mapped and an IOVA of allowed IOVA that can always be mappable.
> 
> The concept of an 'access' refers to something like a VFIO mdev that is
> accessing the IOVA and using a 'struct page *' for CPU based access.
> 
> Externally an API is provided that matches the requirements of the IOCTL
> interface for map/unmap and domain attachment.
> 
> The API provides a 'copy' primitive to establish a new IOVA map in a
> different IOAS from an existing mapping by re-using the iopt_pages. This
> is the basic mechanism to provide single pinning.
> 
> This is designed to support a pre-registration flow where userspace would
> setup an dummy IOAS with no domains, map in memory and then establish
> an
> access to pin all PFNs into the xarray.
> 
> Copy can then be used to create new IOVA mappings in a different IOAS,
> with iommu_domains attached. Upon copy the PFNs will be read out of the
> xarray and mapped into the iommu_domains, avoiding any pin_user_pages()
> overheads.
> 
> Tested-by: Nicolin Chen <nicolinc@nvidia.com>
> Tested-by: Yi Liu <yi.l.liu@intel.com>
> Tested-by: Lixiao Yang <lixiao.yang@intel.com>
> Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>