summaryrefslogtreecommitdiff
path: root/drivers/hv/vmbus_drv.c
diff options
context:
space:
mode:
authorAndrea Parri (Microsoft) <parri.andrea@gmail.com>2020-04-06 02:15:06 +0200
committerWei Liu <wei.liu@kernel.org>2020-04-23 13:17:11 +0000
commit8b6a877c060ed6b86878fe66c7c6493a6054cf23 (patch)
tree530ec7462a01c4021af9c9f5ec81d5a5e64aa8c8 /drivers/hv/vmbus_drv.c
parentb9fa1b8797dcb579a9642a502769e1a5c3adc0d2 (diff)
Drivers: hv: vmbus: Replace the per-CPU channel lists with a global array of channels
When Hyper-V sends an interrupt to the guest, the guest has to figure out which channel the interrupt is associated with. Hyper-V sets a bit in a memory page that is shared with the guest, indicating a particular "relid" that the interrupt is associated with. The current Linux code then uses a set of per-CPU linked lists to map a given "relid" to a pointer to a channel structure. This design introduces a synchronization problem if the CPU that Hyper-V will interrupt for a certain channel is changed. If the interrupt comes on the "old CPU" and the channel was already moved to the per-CPU list of the "new CPU", then the relid -> channel mapping will fail and the interrupt is dropped. Similarly, if the interrupt comes on the new CPU but the channel was not moved to the per-CPU list of the new CPU, then the mapping will fail and the interrupt is dropped. Relids are integers ranging from 0 to 2047. The mapping from relids to channel structures can be done by setting up an array with 2048 entries, each entry being a pointer to a channel structure (hence total size ~16K bytes, which is not a problem). The array is global, so there are no per-CPU linked lists to update. The array can be searched and updated by loading from/storing to the array at the specified index. With no per-CPU data structures, the above mentioned synchronization problem is avoided and the relid2channel() function gets simpler. Suggested-by: Michael Kelley <mikelley@microsoft.com> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com> Link: https://lore.kernel.org/r/20200406001514.19876-4-parri.andrea@gmail.com Reviewed-by: Michael Kelley <mikelley@microsoft.com> Signed-off-by: Wei Liu <wei.liu@kernel.org>
Diffstat (limited to 'drivers/hv/vmbus_drv.c')
-rw-r--r--drivers/hv/vmbus_drv.c48
1 files changed, 29 insertions, 19 deletions
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 1f3e69d18d35..21a01bca7fcd 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1252,33 +1252,39 @@ static void vmbus_chan_sched(struct hv_per_cpu_context *hv_cpu)
if (relid == 0)
continue;
+ /*
+ * Pairs with the kfree_rcu() in vmbus_chan_release().
+ * Guarantees that the channel data structure doesn't
+ * get freed while the channel pointer below is being
+ * dereferenced.
+ */
rcu_read_lock();
/* Find channel based on relid */
- list_for_each_entry_rcu(channel, &hv_cpu->chan_list, percpu_list) {
- if (channel->offermsg.child_relid != relid)
- continue;
+ channel = relid2channel(relid);
+ if (channel == NULL)
+ goto sched_unlock_rcu;
- if (channel->rescind)
- continue;
+ if (channel->rescind)
+ goto sched_unlock_rcu;
- trace_vmbus_chan_sched(channel);
+ trace_vmbus_chan_sched(channel);
- ++channel->interrupts;
+ ++channel->interrupts;
- switch (channel->callback_mode) {
- case HV_CALL_ISR:
- vmbus_channel_isr(channel);
- break;
+ switch (channel->callback_mode) {
+ case HV_CALL_ISR:
+ vmbus_channel_isr(channel);
+ break;
- case HV_CALL_BATCHED:
- hv_begin_read(&channel->inbound);
- /* fallthrough */
- case HV_CALL_DIRECT:
- tasklet_schedule(&channel->callback_event);
- }
+ case HV_CALL_BATCHED:
+ hv_begin_read(&channel->inbound);
+ fallthrough;
+ case HV_CALL_DIRECT:
+ tasklet_schedule(&channel->callback_event);
}
+sched_unlock_rcu:
rcu_read_unlock();
}
}
@@ -2264,9 +2270,12 @@ static int vmbus_bus_suspend(struct device *dev)
list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
/*
- * Invalidate the field. Upon resume, vmbus_onoffer() will fix
- * up the field, and the other fields (if necessary).
+ * Remove the channel from the array of channels and invalidate
+ * the channel's relid. Upon resume, vmbus_onoffer() will fix
+ * up the relid (and other fields, if necessary) and add the
+ * channel back to the array.
*/
+ vmbus_channel_unmap_relid(channel);
channel->offermsg.child_relid = INVALID_RELID;
if (is_hvsock_channel(channel)) {
@@ -2502,6 +2511,7 @@ static void __exit vmbus_exit(void)
hv_debug_rm_all_dir();
vmbus_free_channels();
+ kfree(vmbus_connection.channels);
if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE) {
kmsg_dump_unregister(&hv_kmsg_dumper);