Check that enough time has passed such that the modify channel message
has been processed before taking a CPU offline.
Signed-off-by: Andrea Parri (Microsoft) <parri.and...@gmail.com>
---
drivers/hv/hv.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 49 insertions(+)
diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index 3e6ff83adff42..dc9aa1130b22f 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -15,6 +15,7 @@
#include <linux/hyperv.h>
#include <linux/random.h>
#include <linux/clockchips.h>
+#include <linux/delay.h>
#include <linux/interrupt.h>
#include <clocksource/hyperv_timer.h>
#include <asm/mshyperv.h>
@@ -292,6 +293,41 @@ void hv_synic_disable_regs(unsigned int cpu)
disable_percpu_irq(vmbus_irq);
}
+#define HV_MAX_TRIES 3
+/*
+ * Scan the event flags page of 'this' CPU looking for any bit that is set.
If we find one
+ * bit set, then wait for a few milliseconds. Repeat these steps for a
maximum of 3 times.
+ * Return 'true', if there is still any set bit after this operation; 'false',
otherwise.
+ *
+ * If a bit is set, that means there is a pending channel interrupt. The
expectation is
+ * that the normal interrupt handling mechanism will find and process the
channel interrupt
+ * "very soon", and in the process clear the bit.
+ */
+static bool hv_synic_event_pending(void)
+{
+ struct hv_per_cpu_context *hv_cpu =
this_cpu_ptr(hv_context.cpu_context);
+ union hv_synic_event_flags *event =
+ (union hv_synic_event_flags *)hv_cpu->synic_event_page +
VMBUS_MESSAGE_SINT;
+ unsigned long *recv_int_page = event->flags; /* assumes VMBus version
>= VERSION_WIN8 */
+ bool pending;
+ u32 relid;
+ int tries = 0;
+
+retry:
+ pending = false;
+ for_each_set_bit(relid, recv_int_page, HV_EVENT_FLAGS_COUNT) {
+ /* Special case - VMBus channel protocol messages */
+ if (relid == 0)
+ continue;
+ pending = true;
+ break;
+ }
+ if (pending && tries++ < HV_MAX_TRIES) {
+ usleep_range(10000, 20000);
+ goto retry;
+ }
+ return pending;
+}
int hv_synic_cleanup(unsigned int cpu)
{
@@ -336,6 +372,19 @@ int hv_synic_cleanup(unsigned int cpu)
if (channel_found && vmbus_connection.conn_state == CONNECTED)
return -EBUSY;
+ if (vmbus_proto_version >= VERSION_WIN10_V4_1) {
+ /*
+ * 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.
+ */
+ if (hv_synic_event_pending() && vmbus_connection.conn_state ==
CONNECTED)
+ return -EBUSY;
+ }
+
hv_stimer_legacy_cleanup(cpu);
hv_synic_disable_regs(cpu);
--
2.25.1
