Commit 3a7f7785 authored by Hamza Mahfooz's avatar Hamza Mahfooz Committed by Wei Liu
Browse files

drivers/hv: add CPU offlining support 



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 d570aec0 ("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@gmail.com>
Cc: Michael Kelley <mhklinux@outlook.com>
Cc: Wei Liu <wei.liu@kernel.org>
Signed-off-by: default avatarHamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Reviewed-by: default avatarMichael Kelley <mhklinux@outlook.com>
Tested-by: default avatarMichael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/20250117203309.192072-3-hamzamahfooz@linux.microsoft.com


Signed-off-by: default avatarWei Liu <wei.liu@kernel.org>
Message-ID: <20250117203309.192072-3-hamzamahfooz@linux.microsoft.com>
parent 5e4304ff

drivers/hv/hv.c

+51 −21
Original line number Diff line number Diff line
@@ -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;

}