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

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

[Balbir Singh]

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 <bsingharora@gmail.com>
---
 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

[RFC 2/2] powerpc/mm/memtrace: Let the arch hotunplug code flush cache

[Balbir Singh]

Don't do this via custom code, instead now that we have support
in the arch hotplug/hotunplug code, rely on those routines
to do the right thing.

Signed-off-by: Balbir Singh <bsingharora@gmail.com>
---
 arch/powerpc/platforms/powernv/memtrace.c | 17 -----------------
 1 file changed, 17 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/memtrace.c b/arch/powerpc/platforms/powernv/memtrace.c
index de470caf0784..fc222a0c2ac4 100644
--- a/arch/powerpc/platforms/powernv/memtrace.c
+++ b/arch/powerpc/platforms/powernv/memtrace.c
@@ -82,19 +82,6 @@ static const struct file_operations memtrace_fops = {
 	.open	= simple_open,
 };
 
-static void flush_memory_region(u64 base, u64 size)
-{
-	unsigned long line_size = ppc64_caches.l1d.size;
-	u64 end = base + size;
-	u64 addr;
-
-	base = round_down(base, line_size);
-	end = round_up(end, line_size);
-
-	for (addr = base; addr < end; addr += line_size)
-		asm volatile("dcbf 0,%0" : "=r" (addr) :: "memory");
-}
-
 static int check_memblock_online(struct memory_block *mem, void *arg)
 {
 	if (mem->state != MEM_ONLINE)
@@ -132,10 +119,6 @@ static bool memtrace_offline_pages(u32 nid, u64 start_pfn, u64 nr_pages)
 	walk_memory_range(start_pfn, end_pfn, (void *)MEM_OFFLINE,
 			  change_memblock_state);
 
-	/* RCU grace period? */
-	flush_memory_region((u64)__va(start_pfn << PAGE_SHIFT),
-			    nr_pages << PAGE_SHIFT);
-
 	lock_device_hotplug();
 	remove_memory(nid, start_pfn << PAGE_SHIFT, nr_pages << PAGE_SHIFT);
 	unlock_device_hotplug();
-- 
2.13.6