[PATCH v2 4/8] powerpc/mm: protect linear mapping modifications by a mutex

[David Hildenbrand]

This code currently relies on mem_hotplug_begin()/mem_hotplug_done() -
create_section_mapping()/remove_section_mapping() implementations
cannot tollerate getting called concurrently.

Let's prepare for callers (memtrace) not holding any such locks (and
don't force them to mess with memory hotplug locks).

Other parts in these functions don't seem to rely on external locking.

Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Paul Mackerras <paulus at samba.org>
Cc: Rashmica Gupta <rashmica.g at gmail.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Mike Rapoport <rppt at kernel.org>
Cc: Michal Hocko <mhocko at suse.com>
Cc: Oscar Salvador <osalvador at suse.de>
Cc: Wei Yang <richard.weiyang at linux.alibaba.com>
Signed-off-by: David Hildenbrand <david at redhat.com>
---
 arch/powerpc/mm/mem.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 8a86d81f8df0..ca5c4b54c366 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -58,6 +58,7 @@
 #define CPU_FTR_NOEXECUTE	0
 #endif
 
+static DEFINE_MUTEX(linear_mapping_mutex);
 unsigned long long memory_limit;
 bool init_mem_is_free;
 
@@ -126,8 +127,10 @@ int __ref arch_create_linear_mapping(int nid, u64 start, u64 size,
 	int rc;
 
 	start = (unsigned long)__va(start);
+	mutex_lock(&linear_mapping_mutex);
 	rc = create_section_mapping(start, start + size, nid,
 				    params->pgprot);
+	mutex_unlock(&linear_mapping_mutex);
 	if (rc) {
 		pr_warn("Unable to create linear mapping for 0x%llx..0x%llx: %d\n",
 			start, start + size, rc);
@@ -144,7 +147,9 @@ void __ref arch_remove_linear_mapping(u64 start, u64 size)
 	start = (unsigned long)__va(start);
 	flush_dcache_range_chunked(start, start + size, FLUSH_CHUNK_SIZE);
 
+	mutex_lock(&linear_mapping_mutex);
 	ret = remove_section_mapping(start, start + size);
+	mutex_unlock(&linear_mapping_mutex);
 	WARN_ON_ONCE(ret);
 
 	/* Ensure all vmalloc mappings are flushed in case they also
-- 
2.26.2