Subject: [RFC 1/2] powerpc/mm: Flush cache on memory hot(un)plug

From: Balbir Singh <[email-masked]>
Date: Thu, 5 Apr 2018 21:11:52 +1000

This patch adds support for flushing potentially dirty cache lines when
memory is hot-plugged/hot-un-plugged.  The support is currently limited
to 64 bit systems.

The bug was exposed when mappings for a coherent memory device were
actually hot-unplugged and plugged in back later.  A similar issue was
observed during the development of memtrace, but memtrace does it's own
flushing of region via a custom routine.

These patches do a flush both on hotplug/unplug to clear any stale data
in the cache w.r.t mappings, there is a small race window where a clean
cache line may be created again just prior to tearing down the mapping.
Flushing them on establishment of new mappings helps start with a clean
state.

The patches were tested by disabling the flush routines in memtrace and
doing I/O on the trace file. The system immediately checkstops (quite
reliably, if prior to the hot-unplug of the memtrace region, we memset
the regions we are about to hot unplug). After these patches no custom
flushing is needed in the memtrace code.

Signed-off-by: Balbir Singh <[email-masked]>
---
 arch/powerpc/mm/mem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 85245ef97e72..0a8959b15b39 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -143,6 +143,7 @@ int __meminit arch_add_memory(int nid, u64 start, u64 size, struct vmem_altmap *
 			start, start + size, rc);
 		return -EFAULT;
 	}
+	flush_inval_dcache_range(start, start + size);
 
 	return __add_pages(nid, start_pfn, nr_pages, altmap, want_memblock);
 }
@@ -169,6 +170,7 @@ int __meminit arch_remove_memory(u64 start, u64 size, struct vmem_altmap *altmap
 
 	/* Remove htab bolted mappings for this section of memory */
 	start = (unsigned long)__va(start);
+	flush_inval_dcache_range(start, start + size);
 	ret = remove_section_mapping(start, start + size);
 
 	/* Ensure all vmalloc mappings are flushed in case they also
-- 
2.13.6