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From:   Laurent Dufour <ldufour@linux.ibm.com>
To:     mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org
Cc:     nathanl@linux.ibm.com, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
        Tyrel Datwyler <tyreld@linux.ibm.com>
Subject: [PATCH v4] pseries/drmem: update LMBs after LPM
Date:   Tue,  4 May 2021 11:20:38 +0200
Message-Id: <20210504092038.8514-1-ldufour@linux.ibm.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

After a LPM, the device tree node ibm,dynamic-reconfiguration-memory may be
updated by the hypervisor in the case the NUMA topology of the LPAR's
memory is updated.

This is caught by the kernel, but the memory's node is updated because
there is no way to move a memory block between nodes.

If later a memory block is added or removed, drmem_update_dt() is called
and it is overwriting the DT node to match the added or removed LMB. But
the LMB's associativity node has not been updated after the DT node update
and thus the node is overwritten by the Linux's topology instead of the
hypervisor one.

Introduce a hook called when the ibm,dynamic-reconfiguration-memory node is
updated to force an update of the LMB's associativity. However, ignore the
call to that hook when the update has been triggered by drmem_update_dt().
Because, in that case, the LMB tree has been used to set the DT property
and thus it doesn't need to be updated back. Since drmem_update_dt() is
called under the protection of the device_hotplug_lock and the hook is
called in the same context, use a simple boolean variable to detect that
call.

Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
---

V4:
 - Prevent the LMB to be updated back in the case the request came from the
 LMB tree's update.
V3:
 - Check rd->dn->name instead of rd->dn->full_name
V2:
 - Take Tyrel's idea to rely on OF_RECONFIG_UPDATE_PROPERTY instead of
 introducing a new hook mechanism.
---
 arch/powerpc/include/asm/drmem.h              |  1 +
 arch/powerpc/mm/drmem.c                       | 46 +++++++++++++++++++
 .../platforms/pseries/hotplug-memory.c        |  4 ++
 3 files changed, 51 insertions(+)

diff --git a/arch/powerpc/include/asm/drmem.h b/arch/powerpc/include/asm/drmem.h
index bf2402fed3e0..4265d5e95c2c 100644
--- a/arch/powerpc/include/asm/drmem.h
+++ b/arch/powerpc/include/asm/drmem.h
@@ -111,6 +111,7 @@ int drmem_update_dt(void);
 int __init
 walk_drmem_lmbs_early(unsigned long node, void *data,
 		      int (*func)(struct drmem_lmb *, const __be32 **, void *));
+void drmem_update_lmbs(struct property *prop);
 #endif
 
 static inline void invalidate_lmb_associativity_index(struct drmem_lmb *lmb)
diff --git a/arch/powerpc/mm/drmem.c b/arch/powerpc/mm/drmem.c
index 9af3832c9d8d..22197b18d85e 100644
--- a/arch/powerpc/mm/drmem.c
+++ b/arch/powerpc/mm/drmem.c
@@ -18,6 +18,7 @@ static int n_root_addr_cells, n_root_size_cells;
 
 static struct drmem_lmb_info __drmem_info;
 struct drmem_lmb_info *drmem_info = &__drmem_info;
+static bool in_drmem_update;
 
 u64 drmem_lmb_memory_max(void)
 {
@@ -178,6 +179,11 @@ int drmem_update_dt(void)
 	if (!memory)
 		return -1;
 
+	/*
+	 * Set in_drmem_update to prevent the notifier callback to process the
+	 * DT property back since the change is coming from the LMB tree.
+	 */
+	in_drmem_update = true;
 	prop = of_find_property(memory, "ibm,dynamic-memory", NULL);
 	if (prop) {
 		rc = drmem_update_dt_v1(memory, prop);
@@ -186,6 +192,7 @@ int drmem_update_dt(void)
 		if (prop)
 			rc = drmem_update_dt_v2(memory, prop);
 	}
+	in_drmem_update = false;
 
 	of_node_put(memory);
 	return rc;
@@ -307,6 +314,45 @@ int __init walk_drmem_lmbs_early(unsigned long node, void *data,
 	return ret;
 }
 
+/*
+ * Update the LMB associativity index.
+ */
+static int update_lmb(struct drmem_lmb *updated_lmb,
+		      __maybe_unused const __be32 **usm,
+		      __maybe_unused void *data)
+{
+	struct drmem_lmb *lmb;
+
+	for_each_drmem_lmb(lmb) {
+		if (lmb->drc_index != updated_lmb->drc_index)
+			continue;
+
+		lmb->aa_index = updated_lmb->aa_index;
+		break;
+	}
+	return 0;
+}
+
+/*
+ * Update the LMB associativity index.
+ *
+ * This needs to be called when the hypervisor is updating the
+ * dynamic-reconfiguration-memory node property.
+ */
+void drmem_update_lmbs(struct property *prop)
+{
+	/*
+	 * Don't update the LMBs if triggered by the update done in
+	 * drmem_update_dt(), the LMB values have been used to the update the DT
+	 * property in that case.
+	 */
+	if (in_drmem_update)
+		return;
+	if (!strcmp(prop->name, "ibm,dynamic-memory"))
+		__walk_drmem_v1_lmbs(prop->value, NULL, NULL, update_lmb);
+	else if (!strcmp(prop->name, "ibm,dynamic-memory-v2"))
+		__walk_drmem_v2_lmbs(prop->value, NULL, NULL, update_lmb);
+}
 #endif
 
 static int init_drmem_lmb_size(struct device_node *dn)
diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index 8377f1f7c78e..672ffbee2e78 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -949,6 +949,10 @@ static int pseries_memory_notifier(struct notifier_block *nb,
 	case OF_RECONFIG_DETACH_NODE:
 		err = pseries_remove_mem_node(rd->dn);
 		break;
+	case OF_RECONFIG_UPDATE_PROPERTY:
+		if (!strcmp(rd->dn->name,
+			    "ibm,dynamic-reconfiguration-memory"))
+			drmem_update_lmbs(rd->prop);
 	}
 	return notifier_from_errno(err);
 }
-- 
2.31.1