On Fri, Feb 03, 2023 at 03:25:01PM +0100, Eugenio Pérez wrote:
Starting from an used_idx different than 0 is needed in use cases like
virtual machine migration. Not doing so and letting the caller set an
avail idx different than 0 causes destination device to try to use old
buffers that source driver already recover and are not available
anymore.
Since vdpa_sim does not support receive inflight descriptors as a
destination of a migration, let's set both avail_idx and used_idx the
same at vq start. This is how vhost-user works in a
VHOST_SET_VRING_BASE call.
Although the simple fix is to set last_used_idx at vdpasim_set_vq_state,
it would be reset at vdpasim_queue_ready. The last_avail_idx case is
fixed with commit a09f493c ("vdpa_sim: not reset state in
vdpasim_queue_ready"). Since the only option is to make it equal to
last_avail_idx, adding the only change needed here.
This was discovered and tested live migrating the vdpa_sim_net device.
Fixes: 2c53d0f64c06 ("vdpasim: vDPA device simulator")
Signed-off-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
---
Cherry-picked from patch 2/2 of the series [1]. Differences are:
* Set the value of used_idx at vdpasim_queue_ready instead of fetching
from the guest vring like vhost-kernel.
v2: Actually update last_used_idx only at vdpasim_queue_ready.
Note that commit id present in the patch text is not in master but in
git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git.
[1] https://lkml.org/lkml/2023/1/18/1041
---
drivers/vdpa/vdpa_sim/vdpa_sim.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
index 6a0a65814626..79ac585e40b9 100644
--- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
+++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
@@ -68,6 +68,7 @@ static void vdpasim_queue_ready(struct vdpasim *vdpasim, unsigned int idx)
(uintptr_t)vq->device_addr);
vq->vring.last_avail_idx = last_avail_idx;
+ vq->vring.last_used_idx = last_avail_idx;
vq->vring.notify = vdpasim_vq_notify;
}
-- 2.31.1
If you need to resend, I'd add a comment in the code following the
commit description.
Anyway, the patch LGTM:
Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
Thanks,
Stefano
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