[PATCH 3.2 002/152] powerpc/numa: Fix multiple bugs in memory_hotplug_max()

[Ben Hutchings]

3.2.84-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Bharata B Rao <bharata@xxxxxxxxxxxxxxxxxx>

commit 45b64ee64970dee9392229302efe1d1567e8d304 upstream.

memory_hotplug_max() uses hot_add_drconf_memory_max() to get maxmimum
addressable memory by referring to ibm,dyanamic-memory property. There
are three problems with the current approach:

1 hot_add_drconf_memory_max() assumes that ibm,dynamic-memory includes
  all the LMBs of the guest, but that is not true for PowerKVM which
  populates only DR LMBs (LMBs that can be hotplugged/removed) in that
  property.
2 hot_add_drconf_memory_max() multiplies lmb-size with lmb-count to arrive
  at the max possible address. Since ibm,dynamic-memory doesn't include
  RMA LMBs, the address thus obtained will be less than the actual max
  address. For example, if max possible memory size is 32G, with lmb-size
  of 256MB there can be 127 LMBs in ibm,dynamic-memory (1 LMB for RMA
  which won't be present here).  hot_add_drconf_memory_max() would then
  return the max addressable memory as 127 * 256MB = 31.75GB, the max
  address should have been 32G which is what ibm,lrdr-capacity shows.
3 In PowerKVM, there can be a gap between the end of boot time RAM and
  beginning of hotplug RAM area. So just multiplying lmb-count with
  lmb-size will not provide the correct max possible address for PowerKVM.

This patch fixes 1 by using ibm,lrdr-capacity property to return the max
addressable memory whenever the property is present. Then it fixes 2 & 3
by fetching the address of the last LMB in ibm,dynamic-memory property.

Fixes: cd34206e949b ("powerpc: Add memory_hotplug_max()")
Signed-off-by: Bharata B Rao <bharata@xxxxxxxxxxxxxxxxxx>
Reviewed-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/powerpc/mm/numa.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -1275,17 +1275,33 @@ int hot_add_scn_to_nid(unsigned long scn
 static u64 hot_add_drconf_memory_max(void)
 {
         struct device_node *memory = NULL;
+	struct device_node *dn = NULL;
         unsigned int drconf_cell_cnt = 0;
         u64 lmb_size = 0;
         const u32 *dm = 0;
+	const __be64 *lrdr = NULL;
+	struct of_drconf_cell drmem;
+
+	dn = of_find_node_by_path("/rtas");
+	if (dn) {
+		lrdr = of_get_property(dn, "ibm,lrdr-capacity", NULL);
+		of_node_put(dn);
+		if (lrdr)
+			return be64_to_cpup(lrdr);
+	}
 
         memory = of_find_node_by_path("/ibm,dynamic-reconfiguration-memory");
         if (memory) {
                 drconf_cell_cnt = of_get_drconf_memory(memory, &dm);
                 lmb_size = of_get_lmb_size(memory);
+
+		/* Advance to the last cell, each cell has 6 32 bit integers */
+		dm += (drconf_cell_cnt - 1) * 6;
+		read_drconf_cell(&drmem, &dm);
                 of_node_put(memory);
+		return drmem.base_addr + lmb_size;
         }
-        return lmb_size * drconf_cell_cnt;
+	return 0;
 }
 
 /*