From 8b6a877c060ed6b86878fe66c7c6493a6054cf23 Mon Sep 17 00:00:00 2001 From: "Andrea Parri (Microsoft)" Date: Mon, 6 Apr 2020 02:15:06 +0200 Subject: 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 Signed-off-by: Andrea Parri (Microsoft) Link: https://lore.kernel.org/r/20200406001514.19876-4-parri.andrea@gmail.com Reviewed-by: Michael Kelley Signed-off-by: Wei Liu --- drivers/hv/vmbus_drv.c | 48 +++++++++++++++++++++++++++++------------------- 1 file changed, 29 insertions(+), 19 deletions(-) (limited to 'drivers/hv/vmbus_drv.c') 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); -- cgit v1.2.3