On Thu, 2016-01-28 at 18:55 +0100, Jerome Glisse wrote:
> 
> I would like to attend LSF/MM this year to discuss about HMM
> (Heterogeneous Memory Manager) and more generaly all topics
> related to GPU and heterogeneous memory architecture (including
> persistent memory).
> 
> I want to discuss how to move forward with HMM merging and i
> hope that by MM summit time i will be able to share more
> informations publicly on devices which rely on HMM.

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 patch¹ 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 — 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.

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation


¹ http://www.spinics.net/lists/linux-mm/msg100230.html