Currently, it is tedious to offline CPUs in a Hyper-V VM since CPUs may
have VMBus channels attached to them that a user would have to manually
rebind elsewhere. So, as made mention of in
commit d570aec0f2154 ("Drivers: hv: vmbus: Synchronize init_vp_index()
vs. CPU hotplug"), rebind channels associated with CPUs that a user is
trying to offline to a new "randomly" selected CPU.
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Michael Kelley <mhklinux@xxxxxxxxxxx>
Cc: Wei Liu <wei.liu@xxxxxxxxxx>
Signed-off-by: Hamza Mahfooz <hamzamahfooz@xxxxxxxxxxxxxxxxxxx>
---
v2: remove cpus_read_{un,}lock() from hv_pick_new_cpu() and add
lockdep_assert_cpus_held().
v3: use for_each_cpu_wrap() in hv_pick_new_cpu().
v4: store get_random_u32_below() in start.
v5: style fixes, use target_cpu and set ret to -EBUSY by default.
---
drivers/hv/hv.c | 72 ++++++++++++++++++++++++++++++++++---------------
1 file changed, 51 insertions(+), 21 deletions(-)
diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index 36d9ba097ff5..fab0690b5c41 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -433,13 +433,47 @@ static bool hv_synic_event_pending(void)
return pending;
}
+static int hv_pick_new_cpu(struct vmbus_channel *channel)
+{
+ int ret = -EBUSY;
+ int start;
+ int cpu;
+
+ lockdep_assert_cpus_held();
+ lockdep_assert_held(&vmbus_connection.channel_mutex);
+
+ /*
+ * We can't assume that the relevant interrupts will be sent before
+ * the cpu is offlined on older versions of hyperv.
+ */
+ if (vmbus_proto_version < VERSION_WIN10_V5_3)
+ return -EBUSY;
+
+ start = get_random_u32_below(nr_cpu_ids);
+
+ for_each_cpu_wrap(cpu, cpu_online_mask, start) {
+ if (channel->target_cpu == cpu ||
+ channel->target_cpu == VMBUS_CONNECT_CPU)
+ continue;
+
+ ret = vmbus_channel_set_cpu(channel, cpu);
+ if (!ret)
+ break;
+ }
+
+ if (ret)
+ ret = vmbus_channel_set_cpu(channel, VMBUS_CONNECT_CPU);
+
+ return ret;
+}
+
/*
* hv_synic_cleanup - Cleanup routine for hv_synic_init().
*/
int hv_synic_cleanup(unsigned int cpu)
{
struct vmbus_channel *channel, *sc;
- bool channel_found = false;
+ int ret = 0;
if (vmbus_connection.conn_state != CONNECTED)
goto always_cleanup;
@@ -456,38 +490,34 @@ int hv_synic_cleanup(unsigned int cpu)
/*
* Search for channels which are bound to the CPU we're about to
- * cleanup. In case we find one and vmbus is still connected, we
- * fail; this will effectively prevent CPU offlining.
- *
- * TODO: Re-bind the channels to different CPUs.
+ * cleanup.
*/
mutex_lock(&vmbus_connection.channel_mutex);
list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
if (channel->target_cpu == cpu) {
- channel_found = true;
- break;
+ ret = hv_pick_new_cpu(channel);
+ if (ret) {
+ mutex_unlock(&vmbus_connection.channel_mutex);
+ return ret;
+ }
}
list_for_each_entry(sc, &channel->sc_list, sc_list) {
if (sc->target_cpu == cpu) {
- channel_found = true;
- break;
+ ret = hv_pick_new_cpu(sc);
+ if (ret) {
+ mutex_unlock(&vmbus_connection.channel_mutex);
+ return ret;
+ }
}
}
- if (channel_found)
- break;
}
mutex_unlock(&vmbus_connection.channel_mutex);
- if (channel_found)
- return -EBUSY;
-
/*
- * channel_found == false means that any channels that were previously
- * assigned to the CPU have been reassigned elsewhere with a call of
- * vmbus_send_modifychannel(). Scan the event flags page looking for
- * bits that are set and waiting with a timeout for vmbus_chan_sched()
- * to process such bits. If bits are still set after this operation
- * and VMBus is connected, fail the CPU offlining operation.
+ * Scan the event flags page looking for bits that are set and waiting
+ * with a timeout for vmbus_chan_sched() to process such bits. If bits
+ * are still set after this operation and VMBus is connected, fail the
+ * CPU offlining operation.
*/
if (vmbus_proto_version >= VERSION_WIN10_V4_1 && hv_synic_event_pending())
return -EBUSY;
@@ -497,5 +527,5 @@ int hv_synic_cleanup(unsigned int cpu)
hv_synic_disable_regs(cpu);
- return 0;
+ return ret;
}
--
2.47.1
