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drivers/hv: add CPU offlining support

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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 d570aec0f2 ("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: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/20250117203309.192072-3-hamzamahfooz@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20250117203309.192072-3-hamzamahfooz@linux.microsoft.com>
This commit is contained in:
Hamza Mahfooz 2025-01-17 15:33:08 -05:00 committed by Wei Liu
parent 5e4304ff8c
commit 3a7f7785ea
1 changed files with 51 additions and 21 deletions
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72
drivers/hv/hv.c
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@ -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;
}