Agreed on all points. Nevermind that seems to be missing a user of all
the newly added infrastructure, which should come with the series.
Yep!
I've heard from the people working on NVMe cards that this approach
isn't needed, desired, or correct. I'm deeply skeptical that there
would be an in-kernel user.
Hey Jason,
So regarding NVMe, a possible user for this would be a user-space NVMe
target implementation which wants to use a CMB (controller memory
buffer on the device bar) as an intermediate memory for RDMA. In case
the NVMe unplugs we can't rely on user-space to handle it, and need a
way to tell the HCA to tear down the CMB mappings.
I do think that this problem is solvable if we create a mmu_notitifier
client for this mapping (assuming that device unplug will trigger mmu
invalidate callouts on the relevant pages). But I'm still not exactly
sure how ZONE_DEVICE works with I/O device bar though (I'll appreciate
if someone can educate me here).
CC'ing sbates who played with this stuff at some point...
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