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Subject[PATCH 4.18 022/171] powerpc/memtrace: Remove memory in chunks
Date
4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Rashmica Gupta <rashmica.g@gmail.com>

[ Upstream commit 3f7daf3d7582dc6628ac40a9045dd1bbd80c5f35 ]

When hot-removing memory release_mem_region_adjustable() splits iomem
resources if they are not the exact size of the memory being
hot-deleted. Adding this memory back to the kernel adds a new resource.

Eg a node has memory 0x0 - 0xfffffffff. Hot-removing 1GB from
0xf40000000 results in the single resource 0x0-0xfffffffff being split
into two resources: 0x0-0xf3fffffff and 0xf80000000-0xfffffffff.

When we hot-add the memory back we now have three resources:
0x0-0xf3fffffff, 0xf40000000-0xf7fffffff, and 0xf80000000-0xfffffffff.

This is an issue if we try to remove some memory that overlaps
resources. Eg when trying to remove 2GB at address 0xf40000000,
release_mem_region_adjustable() fails as it expects the chunk of memory
to be within the boundaries of a single resource. We then get the
warning: "Unable to release resource" and attempting to use memtrace
again gives us this error: "bash: echo: write error: Resource
temporarily unavailable"

This patch makes memtrace remove memory in chunks that are always the
same size from an address that is always equal to end_of_memory -
n*size, for some n. So hotremoving and hotadding memory of different
sizes will now not attempt to remove memory that spans multiple
resources.

Signed-off-by: Rashmica Gupta <rashmica.g@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/platforms/powernv/memtrace.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)

--- a/arch/powerpc/platforms/powernv/memtrace.c
+++ b/arch/powerpc/platforms/powernv/memtrace.c
@@ -119,17 +119,15 @@ static bool memtrace_offline_pages(u32 n
walk_memory_range(start_pfn, end_pfn, (void *)MEM_OFFLINE,
change_memblock_state);

- lock_device_hotplug();
- remove_memory(nid, start_pfn << PAGE_SHIFT, nr_pages << PAGE_SHIFT);
- unlock_device_hotplug();

return true;
}

static u64 memtrace_alloc_node(u32 nid, u64 size)
{
- u64 start_pfn, end_pfn, nr_pages;
+ u64 start_pfn, end_pfn, nr_pages, pfn;
u64 base_pfn;
+ u64 bytes = memory_block_size_bytes();

if (!node_spanned_pages(nid))
return 0;
@@ -142,8 +140,21 @@ static u64 memtrace_alloc_node(u32 nid,
end_pfn = round_down(end_pfn - nr_pages, nr_pages);

for (base_pfn = end_pfn; base_pfn > start_pfn; base_pfn -= nr_pages) {
- if (memtrace_offline_pages(nid, base_pfn, nr_pages) == true)
+ if (memtrace_offline_pages(nid, base_pfn, nr_pages) == true) {
+ /*
+ * Remove memory in memory block size chunks so that
+ * iomem resources are always split to the same size and
+ * we never try to remove memory that spans two iomem
+ * resources.
+ */
+ lock_device_hotplug();
+ end_pfn = base_pfn + nr_pages;
+ for (pfn = base_pfn; pfn < end_pfn; pfn += bytes>> PAGE_SHIFT) {
+ remove_memory(nid, pfn << PAGE_SHIFT, bytes);
+ }
+ unlock_device_hotplug();
return base_pfn << PAGE_SHIFT;
+ }
}

return 0;

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