Re: [PATCH RFC 00/12] IOMMUFD Generic interface

From: Eric Auger <eric.auger@redhat.com>
To: Jason Gunthorpe <jgg@nvidia.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>,
	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>,
	Yi Liu <yi.l.liu@intel.com>, Keqian Zhu <zhukeqian1@huawei.com>
Subject: Re: [PATCH RFC 00/12] IOMMUFD Generic interface
Date: Tue, 12 Apr 2022 22:50:32 +0200	[thread overview]
Message-ID: <80cceffd-6213-7c85-e50a-71b931bd0b80@redhat.com> (raw)
In-Reply-To: <20220412202239.GL2120790@nvidia.com>

Hi Jason,

On 4/12/22 10:22 PM, Jason Gunthorpe wrote:
> On Tue, Apr 12, 2022 at 10:13:32PM +0200, Eric Auger wrote:
>> Hi,
>>
>> On 3/18/22 6:27 PM, Jason Gunthorpe wrote:
>>> iommufd is the user API to control the IOMMU subsystem as it relates to
>>> managing IO page tables that point at user space memory.
>>>
>>> It takes over from drivers/vfio/vfio_iommu_type1.c (aka the VFIO
>>> container) which is the VFIO specific interface for a similar idea.
>>>
>>> We see a broad need for extended features, some being highly IOMMU device
>>> specific:
>>>  - Binding iommu_domain's to PASID/SSID
>>>  - Userspace page tables, for ARM, x86 and S390
>>>  - Kernel bypass'd invalidation of user page tables
>>>  - Re-use of the KVM page table in the IOMMU
>>>  - Dirty page tracking in the IOMMU
>>>  - Runtime Increase/Decrease of IOPTE size
>>>  - PRI support with faults resolved in userspace
>> This series does not have any concept of group fds anymore and the API
>> is device oriented.
>> I have a question wrt pci bus reset capability.
>>
>> 8b27ee60bfd6 ("vfio-pci: PCI hot reset interface")
>> introduced VFIO_DEVICE_PCI_GET_HOT_RESET_INFO and VFIO_DEVICE_PCI_HOT_RESET
>>
>> Maybe we can reuse VFIO_DEVICE_GET_PCI_HOT_RESET_INFO to retrieve the devices and iommu groups that need to be checked and involved in the bus reset. If I understand correctly we now need to make sure the devices are handled in the same security context (bound to the same iommufd)
>>
>> however VFIO_DEVICE_PCI_HOT_RESET operate on a collection of group fds.
>>
>> How do you see the porting of this functionality onto /dev/iommu?
> I already made a patch that converts VFIO_DEVICE_PCI_HOT_RESET to work
> on a generic notion of a file and the underlying infrastructure to
> allow it to accept either a device or group fd.
>
> Same for the similar issue in KVM.
>
> It is part of three VFIO series I will be posting. First is up here:
>
> https://lore.kernel.org/kvm/0-v1-a8faf768d202+125dd-vfio_mdev_no_group_jgg@nvidia.com/
>
> Overall the strategy is to contain the vfio_group as an internal detail
> of vfio.ko and external interfaces use either a struct vfio_device *
> or a struct file *
Thank you for the quick reply. Yi and I will look at this series. I
guess we won't support the bus reset functionality in our first QEMU
porting onto /dev/iommu until that code stabilizes.

Eric
>
> Jason
>