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| author | Andrea Parri (Microsoft) <parri.andrea@gmail.com> | 2020-04-06 02:15:06 +0200 |
|---|---|---|
| committer | Wei Liu <wei.liu@kernel.org> | 2020-04-23 13:17:11 +0000 |
| commit | 8b6a877c060ed6b86878fe66c7c6493a6054cf23 (patch) | |
| tree | 530ec7462a01c4021af9c9f5ec81d5a5e64aa8c8 /drivers/hv/hv.c | |
| parent | b9fa1b8797dcb579a9642a502769e1a5c3adc0d2 (diff) | |
| download | linux-8b6a877c060ed6b86878fe66c7c6493a6054cf23.tar.bz2 | |
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/hv.c')
| -rw-r--r-- | drivers/hv/hv.c | 2 |
1 files changed, 0 insertions, 2 deletions
diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c index e2b331045464..17bf1f229152 100644 --- a/drivers/hv/hv.c +++ b/drivers/hv/hv.c @@ -117,8 +117,6 @@ int hv_synic_alloc(void) pr_err("Unable to allocate post msg page\n"); goto err; } - - INIT_LIST_HEAD(&hv_cpu->chan_list); } return 0; |