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authorAndrea Parri (Microsoft) <parri.andrea@gmail.com>2020-04-06 03:15:06 +0300
committerWei Liu <wei.liu@kernel.org>2020-04-23 16:17:11 +0300
commit8b6a877c060ed6b86878fe66c7c6493a6054cf23 (patch)
tree530ec7462a01c4021af9c9f5ec81d5a5e64aa8c8 /drivers/hv/connection.c
parentb9fa1b8797dcb579a9642a502769e1a5c3adc0d2 (diff)
downloadlinux-8b6a877c060ed6b86878fe66c7c6493a6054cf23.tar.xz
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/connection.c')
-rw-r--r--drivers/hv/connection.c38
1 files changed, 11 insertions, 27 deletions
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index f4bd306d2cef..11170d9a2e1a 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -248,6 +248,14 @@ int vmbus_connect(void)
pr_info("Vmbus version:%d.%d\n",
version >> 16, version & 0xFFFF);
+ vmbus_connection.channels = kcalloc(MAX_CHANNEL_RELIDS,
+ sizeof(struct vmbus_channel *),
+ GFP_KERNEL);
+ if (vmbus_connection.channels == NULL) {
+ ret = -ENOMEM;
+ goto cleanup;
+ }
+
kfree(msginfo);
return 0;
@@ -295,33 +303,9 @@ void vmbus_disconnect(void)
*/
struct vmbus_channel *relid2channel(u32 relid)
{
- struct vmbus_channel *channel;
- struct vmbus_channel *found_channel = NULL;
- struct list_head *cur, *tmp;
- struct vmbus_channel *cur_sc;
-
- BUG_ON(!mutex_is_locked(&vmbus_connection.channel_mutex));
-
- list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
- if (channel->offermsg.child_relid == relid) {
- found_channel = channel;
- break;
- } else if (!list_empty(&channel->sc_list)) {
- /*
- * Deal with sub-channels.
- */
- list_for_each_safe(cur, tmp, &channel->sc_list) {
- cur_sc = list_entry(cur, struct vmbus_channel,
- sc_list);
- if (cur_sc->offermsg.child_relid == relid) {
- found_channel = cur_sc;
- break;
- }
- }
- }
- }
-
- return found_channel;
+ if (WARN_ON(relid >= MAX_CHANNEL_RELIDS))
+ return NULL;
+ return READ_ONCE(vmbus_connection.channels[relid]);
}
/*