Hey,

On Wed, Feb 03, 2016 at 12:40:57AM +0000, David Woodhouse wrote:

There are a few related issues here around Shared Virtual Memory, and
lifetime management of the associated MM, and the proposal discussed at
the Kernel Summit for "off-CPU tasks".

I've hit a situation with the Intel SVM code in 4.4 where the device
driver binds a PASID, and also has mmap() functionality on the same
file descriptor that the PASID is associated with.

So on process exit, the MM doesn't die because the PASID binding still
exists. The VMA of the mmap doesn't die because the MM still exists. So
the underlying file remains open because the VMA still exists. And the
PASID binding thus doesn't die because the file is still open.

I've posted a patchA1 which moves us closer to the amd_iommu_v2 model,
although I'm still *strongly* resisting the temptation to call out into
device driver code from the mmu_notifier's release callback.

I would like to attend LSF/MM this year so we can continue to work on
those issues a?? now that we actually have some hardware in the field and
a better idea of how we can build a unified access model for SVM across
the different IOMMU types.

That sounds very interesting and I'd like to participate in this
discussion. Unfortunatly I can't make it to the mm-sumit this year, so I
didn't even apply for an invitation.

But if this gets discussed there I am interested in the outcome. I still
have a prototype for the off-cpu task concept on my list of thing to
implement. The problem is that I can't really test any changes I make
because I don't have SVM hardware and on the AMD side the user-space
part needed for testing only runs on Ubuntu with some AMD provided
kernel :(


	Joerg

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