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From: Jason Gunthorpe <jgg@nvidia.com>
To: "Tian, Kevin" <kevin.tian@intel.com>
Cc: Alex Williamson <alex.williamson@redhat.com>,
	"cohuck@redhat.com" <cohuck@redhat.com>,
	"corbet@lwn.net" <corbet@lwn.net>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"farman@linux.ibm.com" <farman@linux.ibm.com>,
	"mjrosato@linux.ibm.com" <mjrosato@linux.ibm.com>,
	"pasic@linux.ibm.com" <pasic@linux.ibm.com>,
	"Lu, Baolu" <baolu.lu@intel.com>
Subject: Re: [RFC PATCH] vfio: Update/Clarify migration uAPI, add NDMA state
Date: Tue, 4 Jan 2022 12:09:59 -0400	[thread overview]
Message-ID: <20220104160959.GJ2328285@nvidia.com> (raw)
In-Reply-To: <BN9PR11MB5276145C1D82FAFBDCF70AEF8C4A9@BN9PR11MB5276.namprd11.prod.outlook.com>

On Tue, Jan 04, 2022 at 03:49:07AM +0000, Tian, Kevin wrote:
 
> btw can you elaborate the DOS concern? The device is assigned
> to an user application, which has one thread (migration thread)
> blocked on another thread (vcpu thread) when transiting the
> device to NDMA state. What service outside of this application
> is denied here?

The problem is the VM controls when the vPRI is responded and
migration cannot proceed until this is done.

So the basic DOS is for a hostile VM to trigger a vPRI and then never
answer it. Even trivially done from userspace with a vSVA and
userfaultfd, for instance.

This will block the hypervisor from ever migrating the VM in a very
poor way - it will just hang in the middle of a migration request.

Regardless of the complaints of the IP designers, this is a very poor
direction.

Progress in the hypervisor should never be contingent on a guest VM.

Jason

  reply	other threads:[~2022-01-04 16:10 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-09 23:34 [RFC PATCH] vfio: Update/Clarify migration uAPI, add NDMA state Alex Williamson
2021-12-10  1:25 ` Jason Gunthorpe
2021-12-13 20:40   ` Alex Williamson
2021-12-14 12:08     ` Cornelia Huck
2021-12-14 16:26     ` Jason Gunthorpe
2021-12-20 22:26       ` Alex Williamson
2022-01-04 20:28         ` Jason Gunthorpe
2022-01-06 18:17           ` Alex Williamson
2022-01-06 21:20             ` Jason Gunthorpe
2022-01-10  7:55               ` Tian, Kevin
2022-01-10 17:34                 ` Alex Williamson
2022-01-11  2:41                   ` Tian, Kevin
2022-01-10 18:11                 ` Jason Gunthorpe
2022-01-11  3:14                   ` Tian, Kevin
2022-01-11 18:19                     ` Jason Gunthorpe
2022-01-04  3:49       ` Tian, Kevin
2022-01-04 16:09         ` Jason Gunthorpe [this message]
2022-01-05  1:59           ` Tian, Kevin
2022-01-05 12:45             ` Jason Gunthorpe
2022-01-06  6:32               ` Tian, Kevin
2022-01-06 15:42                 ` Jason Gunthorpe
2022-01-07  0:00                   ` Tian, Kevin
2022-01-07  0:29                     ` Jason Gunthorpe
2022-01-07  2:01                       ` Tian, Kevin
2022-01-07 17:23                         ` Jason Gunthorpe
2022-01-10  3:14                           ` Tian, Kevin
2022-01-10 17:52                             ` Jason Gunthorpe
2022-01-11  2:57                               ` Tian, Kevin
2022-01-05  3:06           ` Tian, Kevin
2021-12-20 17:38 ` Cornelia Huck
2021-12-20 22:49   ` Alex Williamson
2021-12-21 11:24     ` Cornelia Huck
2022-01-07  8:03 ` Tian, Kevin
2022-01-07 16:36   ` Alex Williamson
2022-01-10  6:01     ` Tian, Kevin

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