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author | Bharata B Rao <bharata@linux.ibm.com> | 2020-07-09 18:49:24 +0530 |
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committer | Michael Ellerman <mpe@ellerman.id.au> | 2020-07-20 22:57:56 +1000 |
commit | d6d6ebfc5dbb4008be21baa4ec2ad45606578966 (patch) | |
tree | 3c390a7e93880692b0a8553da11bb894738ef09d /arch/powerpc/platforms | |
parent | 9ce8853b4a735c8115f55ac0e9c2b27a4c8f80b5 (diff) | |
download | linux-d6d6ebfc5dbb4008be21baa4ec2ad45606578966.tar.bz2 |
powerpc/mm/radix: Remove split_kernel_mapping()
We split the page table mapping on memory unplug if the
linear range was mapped with huge page mapping (for ex: 1G)
The page table splitting code has a few issues:
1. Recursive locking
--------------------
Memory unplug path takes cpu_hotplug_lock and calls stop_machine()
for splitting the mappings. However stop_machine() takes
cpu_hotplug_lock again causing deadlock.
2. BUG: sleeping function called from in_atomic() context
---------------------------------------------------------
Memory unplug path (remove_pagetable) takes init_mm.page_table_lock
spinlock and later calls stop_machine() which does wait_for_completion()
3. Bad unlock unbalance
-----------------------
Memory unplug path takes init_mm.page_table_lock spinlock and calls
stop_machine(). The stop_machine thread function runs in a different
thread context (migration thread) which tries to release and reaquire
ptl. Releasing ptl from a different thread than which acquired it
causes bad unlock unbalance.
These problems can be avoided if we avoid mapping hot-plugged memory
with 1G mapping, thereby removing the need for splitting them during
unplug. The kernel always make sure the minimum unplug request is
SUBSECTION_SIZE for device memory and SECTION_SIZE for regular memory.
In preparation for such a change remove page table splitting support.
This essentially is a revert of
commit 4dd5f8a99e791 ("powerpc/mm/radix: Split linear mapping on hot-unplug")
Signed-off-by: Bharata B Rao <bharata@linux.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200709131925.922266-4-aneesh.kumar@linux.ibm.com
Diffstat (limited to 'arch/powerpc/platforms')
0 files changed, 0 insertions, 0 deletions