** Changed in: linux (Ubuntu)
Status: In Progress => Invalid
** Changed in: linux (Ubuntu Artful)
Assignee: (unassigned) => Colin Ian King (colin-king)
** Changed in: linux (Ubuntu)
Assignee: Colin Ian King (colin-king) => (unassigned)
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https://bugs.launchpad.net/bugs/1761104
Title:
fix regression in mm/hotplug, allows NVIDIA driver to work
Status in linux package in Ubuntu:
Invalid
Status in linux source package in Artful:
Fix Committed
Bug description:
== SRU Justification, ARTFUL ==
Bug fix #1747069 causes an issue for NVIDIA drivers on ppc64el
platforms. According to Will Davis at NVIDIA:
"- The original patch 3d79a728f9b2e6ddcce4e02c91c4de1076548a4c changed
the call to arch_add_memory in mm/memory_hotplug.c to call with the
boolean argument set to true instead of false, and inverted the
semantics of that argument in the arch layers.
- The revert patch 4fe85d5a7c50f003fe4863a1a87f5d8cc121c75c reverted
the semantic change in the arch layers, but didn't revert the change
to the arch_add_memory call in mm/memory_hotplug.c"
And also:
"It looks like the problem here is that the online_type is _MOVABLE but
can_online_high_movable(nid=255) is returning false:
if ((zone_idx(zone) > ZONE_NORMAL ||
online_type == MMOP_ONLINE_MOVABLE) &&
!can_online_high_movable(pfn_to_nid(pfn)))
This check was removed by upstream commit
57c0a17238e22395428248c53f8e390c051c88b8, and I've verified that if I apply
that commit (partially) to the 4.13.0-37.42 tree along with the previous
arch_add_memory patch to make the probe work, I can fully online the GPU
device
memory as expected.
Commit 57c0a172.. implies that the can_online_high_movable() checks weren't
useful anyway, so in addition to the arch_add_memory fix, does it make sense
to
revert the pieces of 4fe85d5a7c50f003fe4863a1a87f5d8cc121c75c that added back
the can_online_high_movable() check?"
== Fix ==
Fix partial backport from bug #1747069, remove can_online_high_movable
and fix the incorrectly set boolean argument to arch_add_memory().
== Testing ==
run ADT memory hotplug test, should not regress this. Without the fix,
the nvidia driver on powerpc will not load because it cannot map
memory for the device. With the fix it loads.
== Regression Potential ==
This fixes a regression in the original fix and hence the regression
potential is the same as the previously SRU'd bug fix for #1747069,
namely:
"Reverting this commit does remove some functionality, however this
does not regress the kernel compared to previous releases and having a
working reliable memory hotplug is the preferred option. This fix does
touch some memory hotplug, so there is a risk that this may break this
functionality that is not covered by the kernel regression testing."
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