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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <PH0PR12MB54811863B392C644E5365446DC3E9@PH0PR12MB5481.namprd12.prod.outlook.com>
Date:   Tue, 1 Jun 2021 17:30:51 +0000
From:   Parav Pandit <parav@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Alex Williamson (alex.williamson@...hat.com)" 
        <alex.williamson@...hat.com>, Jason Wang <jasowang@...hat.com>
CC:     Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Robin Murphy <robin.murphy@....com>
Subject: RE: [RFC] /dev/ioasid uAPI proposal

> From: Tian, Kevin <kevin.tian@...el.com>
> Sent: Thursday, May 27, 2021 1:28 PM

> 5.6. I/O page fault
> +++++++++++++++
> 
> (uAPI is TBD. Here is just about the high-level flow from host IOMMU driver
> to guest IOMMU driver and backwards).
> 
> -   Host IOMMU driver receives a page request with raw fault_data {rid,
>     pasid, addr};
> 
> -   Host IOMMU driver identifies the faulting I/O page table according to
>     information registered by IOASID fault handler;
> 
> -   IOASID fault handler is called with raw fault_data (rid, pasid, addr), which
>     is saved in ioasid_data->fault_data (used for response);
> 
> -   IOASID fault handler generates an user fault_data (ioasid, addr), links it
>     to the shared ring buffer and triggers eventfd to userspace;
> 
> -   Upon received event, Qemu needs to find the virtual routing information
>     (v_rid + v_pasid) of the device attached to the faulting ioasid. If there are
>     multiple, pick a random one. This should be fine since the purpose is to
>     fix the I/O page table on the guest;
> 
> -   Qemu generates a virtual I/O page fault through vIOMMU into guest,
>     carrying the virtual fault data (v_rid, v_pasid, addr);
> 
Why does it have to be through vIOMMU?
For a VFIO PCI device, have you considered to reuse the same PRI interface to inject page fault in the guest?
This eliminates any new v_rid.
It will also route the page fault request and response through the right vfio device.

> -   Guest IOMMU driver fixes up the fault, updates the I/O page table, and
>     then sends a page response with virtual completion data (v_rid, v_pasid,
>     response_code) to vIOMMU;
> 
What about fixing up the fault for mmu page table as well in guest?
Or you meant both when above you said "updates the I/O page table"?

It is unclear to me that if there is single nested page table maintained or two (one for cr3 references and other for iommu).
Can you please clarify?

> -   Qemu finds the pending fault event, converts virtual completion data
>     into (ioasid, response_code), and then calls a /dev/ioasid ioctl to
>     complete the pending fault;
> 
For VFIO PCI device a virtual PRI request response interface is done, it can be generic interface among multiple vIOMMUs.

> -   /dev/ioasid finds out the pending fault data {rid, pasid, addr} saved in
>     ioasid_data->fault_data, and then calls iommu api to complete it with
>     {rid, pasid, response_code};
>