[PULL 02/19] spapr.c: add 'name' property for hotplugged CPUs nodes

From: David Gibson <david@gibson.dropbear.id.au>
To: peter.maydell@linaro.org, groug@kaod.org
Cc: Daniel Henrique Barboza <danielhb413@gmail.com>,
	qemu-ppc@nongnu.org, qemu-devel@nongnu.org,
	David Gibson <david@gibson.dropbear.id.au>
Subject: [PULL 02/19] spapr.c: add 'name' property for hotplugged CPUs nodes
Date: Wed, 10 Feb 2021 17:17:18 +1100	[thread overview]
Message-ID: <20210210061735.304384-3-david@gibson.dropbear.id.au> (raw)
In-Reply-To: <20210210061735.304384-1-david@gibson.dropbear.id.au>

From: Daniel Henrique Barboza <danielhb413@gmail.com>

In the CPU hotunplug bug [1] the guest kernel throws a scary
message in dmesg:

pseries-hotplug-cpu: Failed to offline CPU <NULL>, rc: -16

The reason isn't related to the bug though. This happens because the
kernel file arch/powerpc/platform/pseries/hotplug-cpu.c, function
dlpar_cpu_remove(), is not finding the device_node.name of the offending
CPU.

We're not populating the 'name' property for hotplugged CPUs. Since the
kernel relies on device_node.name for identifying CPU nodes, and the
CPUs that are coldplugged has the 'name' property filled by SLOF, this
is creating an unneeded inconsistency between hotplug and coldplug CPUs
in the kernel.

Let's fill the 'name' property for hotplugged CPUs as well. This will
make the guest dmesg throws a less intimidating message when we try to
unplug the last online CPU:

pseries-hotplug-cpu: Failed to offline CPU PowerPC,POWER9@1, rc: -16

[1] https://bugzilla.redhat.com/1911414

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20210120232305.241521-3-danielhb413@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 hw/ppc/spapr.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index e7992c0422..0ecc193468 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -3756,6 +3756,19 @@ int spapr_core_dt_populate(SpaprDrc *drc, SpaprMachineState *spapr,
 
     spapr_dt_cpu(cs, fdt, offset, spapr);
 
+    /*
+     * spapr_dt_cpu() does not fill the 'name' property in the
+     * CPU node. The function is called during boot process, before
+     * and after CAS, and overwriting the 'name' property written
+     * by SLOF is not allowed.
+     *
+     * Write it manually after spapr_dt_cpu(). This makes the hotplug
+     * CPUs more compatible with the coldplugged ones, which have
+     * the 'name' property. Linux Kernel also relies on this
+     * property to identify CPU nodes.
+     */
+    _FDT((fdt_setprop_string(fdt, offset, "name", nodename)));
+
     *fdt_start_offset = offset;
     return 0;
 }
-- 
2.29.2


