Messages in this thread Patch in this message | | | From | Eugenio Pérez <> | Subject | [PATCH v3] vdpa_sim: set last_used_idx as last_avail_idx in vdpasim_queue_ready | Date | Thu, 2 Mar 2023 19:18:57 +0100 |
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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 0e84f918fac8 ("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") Reviewed-by: Stefano Garzarella <sgarzare@redhat.com> Signed-off-by: Eugenio Pérez <eperezma@redhat.com> --- 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.
v3: * Fix commit id in the patch message. * Add in code comment following the patch message about why it is done this way. 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 | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c index 6a0a65814626..eea23c630f7c 100644 --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c @@ -68,6 +68,17 @@ static void vdpasim_queue_ready(struct vdpasim *vdpasim, unsigned int idx) (uintptr_t)vq->device_addr); vq->vring.last_avail_idx = last_avail_idx; + + /* + * 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. + */ + vq->vring.last_used_idx = last_avail_idx; vq->vring.notify = vdpasim_vq_notify; } -- 2.31.1
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