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Subject[PATCH v2 0/8] powernv/memtrace: don't abuse memory hot(un)plug infrastructure for memory allocations
Date
Based on latest linux/master

powernv/memtrace is the only in-kernel user that rips out random memory
it never added (doesn't own) in order to allocate memory without a
linear mapping. Let's stop abusing memory hot(un)plug infrastructure for
that - use alloc_contig_pages() for allocating memory and remove the
linear mapping manually.

The original idea was discussed in:
https://lkml.kernel.org/r/48340e96-7e6b-736f-9e23-d3111b915b6e@redhat.com

I only tested via QEMU TCG with a single NUMA node- see patch #8 for more
details.

Error handling and cleanup handling in memtrace code is a mess - that
should definitely get cleaned up sooner or later. Once we have __GFP_ZERO
support for alloc_contig_pages(), we can drop manual clearing. I added
a TODO for now, so this series can go via the powerpc tree - the __GFP_ZERO
change is then better suited via the mm tree, along with support for
__GFP_ZERO.

v1 -> v2:
- Tweaks to patch descriptions
- "powernv/memtrace: don't leak kernel memory to user space"
-- Added. Reported by Michael.
- "powernv/memtrace: fix crashing the kernel when enabling concurrently"
-- Added, discovered while testing.
- "powerpc/mm: protect linear mapping modifications by a mutex"
-- Added. Although we currently won't have concurrency, this is cleaner and
future-proof.
- "powerepc/book3s64/hash: drop WARN_ON in hash__remove_section_mapping"
-- Added. Suggested by Oscar
- "powernv/memtrace: don't abuse memory hot(un)plug infrastructure for
memory allocations"
-- Reshuffle the code to make review easier.
-- Add a TODO regarding __GFP_ZERO. Adapt to changed page clearing code.
-- Use GFP_KERNEL | __GFP_THISNODE | __GFP_NOWARN for allocations.


David Hildenbrand (8):
powernv/memtrace: don't leak kernel memory to user space
powernv/memtrace: fix crashing the kernel when enabling concurrently
powerpc/mm: factor out creating/removing linear mapping
powerpc/mm: protect linear mapping modifications by a mutex
powerpc/mm: print warning in arch_remove_linear_mapping()
powerepc/book3s64/hash: drop WARN_ON in hash__remove_section_mapping
powerpc/mm: remove linear mapping if __add_pages() fails in
arch_add_memory()
powernv/memtrace: don't abuse memory hot(un)plug infrastructure for
memory allocations

arch/powerpc/mm/book3s64/hash_utils.c | 1 -
arch/powerpc/mm/mem.c | 53 +++++--
arch/powerpc/platforms/powernv/Kconfig | 8 +-
arch/powerpc/platforms/powernv/memtrace.c | 175 ++++++++++------------
include/linux/memory_hotplug.h | 3 +
5 files changed, 125 insertions(+), 115 deletions(-)

--
2.26.2

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