linux-kernel - [PATCH 4.14 69/91] powerpc/mm: Flush cache on memory hot(un)plug

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Date:   Mon, 30 Apr 2018 12:24:51 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Balbir Singh <bsingharora@...il.com>,
        Reza Arbab <arbab@...ux.ibm.com>,
        Rashmica Gupta <rashmica.g@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 4.14 69/91] powerpc/mm: Flush cache on memory hot(un)plug

4.14-stable review patch.  If anyone has any objections, please let me know.

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

From: Balbir Singh <bsingharora@...il.com>

commit fb5924fddf9ee31db04da7ad4e8c3434a387101b upstream.

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 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.

The patches were tested by disabling the flush routines in memtrace
and doing I/O on the trace file. The system immediately
checkstops (quite reliablly 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.

Fixes: 9d5171a8f248 ("powerpc/powernv: Enable removal of memory for in memory tracing")
Cc: stable@...r.kernel.org # v4.14+
Signed-off-by: Balbir Singh <bsingharora@...il.com>
Acked-by: Reza Arbab <arbab@...ux.ibm.com>
Reviewed-by: Rashmica Gupta <rashmica.g@...il.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/powerpc/mm/mem.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -143,6 +143,7 @@ int arch_add_memory(int nid, u64 start,
 			start, start + size, rc);
 		return -EFAULT;
 	}
+	flush_inval_dcache_range(start, start + size);

 	return __add_pages(nid, start_pfn, nr_pages, want_memblock);
 }
@@ -171,6 +172,7 @@ int arch_remove_memory(u64 start, u64 si

 	/* 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