Re: [PATCH v2 02/14] vhost: Add Shadow VirtQueue kick forwarding capabilities

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在 2022/3/2 上午2:49, Eugenio Perez Martin 写道:
On Mon, Feb 28, 2022 at 3:57 AM Jason Wang<jasowang@xxxxxxxxxx>  wrote:
在 2022/2/27 下午9:40, Eugenio Pérez 写道:
At this mode no buffer forwarding will be performed in SVQ mode: Qemu
will just forward the guest's kicks to the device.

Host memory notifiers regions are left out for simplicity, and they will
not be addressed in this series.

Signed-off-by: Eugenio Pérez<eperezma@xxxxxxxxxx>
---
   hw/virtio/vhost-shadow-virtqueue.h |  14 +++
   include/hw/virtio/vhost-vdpa.h     |   4 +
   hw/virtio/vhost-shadow-virtqueue.c |  52 +++++++++++
   hw/virtio/vhost-vdpa.c             | 145 ++++++++++++++++++++++++++++-
   4 files changed, 213 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h
index f1519e3c7b..1cbc87d5d8 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -18,8 +18,22 @@ typedef struct VhostShadowVirtqueue {
       EventNotifier hdev_kick;
       /* Shadow call notifier, sent to vhost */
       EventNotifier hdev_call;
+
+    /*
+     * Borrowed virtqueue's guest to host notifier. To borrow it in this event
+     * notifier allows to recover the VhostShadowVirtqueue from the event loop
+     * easily. If we use the VirtQueue's one, we don't have an easy way to
+     * retrieve VhostShadowVirtqueue.
+     *
+     * So shadow virtqueue must not clean it, or we would lose VirtQueue one.
+     */
+    EventNotifier svq_kick;
   } VhostShadowVirtqueue;

+void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd);
+
+void vhost_svq_stop(VhostShadowVirtqueue *svq);
+
   VhostShadowVirtqueue *vhost_svq_new(void);

   void vhost_svq_free(gpointer vq);
diff --git a/include/hw/virtio/vhost-vdpa.h b/include/hw/virtio/vhost-vdpa.h
index 3ce79a646d..009a9f3b6b 100644
--- a/include/hw/virtio/vhost-vdpa.h
+++ b/include/hw/virtio/vhost-vdpa.h
@@ -12,6 +12,8 @@
   #ifndef HW_VIRTIO_VHOST_VDPA_H
   #define HW_VIRTIO_VHOST_VDPA_H

+#include <gmodule.h>
+
   #include "hw/virtio/virtio.h"
   #include "standard-headers/linux/vhost_types.h"

@@ -27,6 +29,8 @@ typedef struct vhost_vdpa {
       bool iotlb_batch_begin_sent;
       MemoryListener listener;
       struct vhost_vdpa_iova_range iova_range;
+    bool shadow_vqs_enabled;
+    GPtrArray *shadow_vqs;
       struct vhost_dev *dev;
       VhostVDPAHostNotifier notifier[VIRTIO_QUEUE_MAX];
   } VhostVDPA;
diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 019cf1950f..a5d0659f86 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -11,6 +11,56 @@
   #include "hw/virtio/vhost-shadow-virtqueue.h"

   #include "qemu/error-report.h"
+#include "qemu/main-loop.h"
+#include "linux-headers/linux/vhost.h"
+
+/** Forward guest notifications */
+static void vhost_handle_guest_kick(EventNotifier *n)
+{
+    VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue,
+                                             svq_kick);
+    event_notifier_test_and_clear(n);
+    event_notifier_set(&svq->hdev_kick);
+}
+
+/**
+ * Set a new file descriptor for the guest to kick the SVQ and notify for avail
+ *
+ * @svq          The svq
+ * @svq_kick_fd  The svq kick fd
+ *
+ * Note that the SVQ will never close the old file descriptor.
+ */
+void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd)
+{
+    EventNotifier *svq_kick = &svq->svq_kick;
+    bool poll_stop = VHOST_FILE_UNBIND != event_notifier_get_fd(svq_kick);
I wonder if this is robust. E.g is there any chance that may end up with
both poll_stop and poll_start are false?

I cannot make that happen in qemu, but the function supports that case
well: It will do nothing. It's more or less the same code as used in
the vhost kernel, and is the expected behaviour if you send two
VHOST_FILE_UNBIND one right after another to me.


I would think it's just stop twice.



If not, can we simple detect poll_stop as below and treat !poll_start
and poll_stop?

I'm not sure what does it add. Is there an unexpected consequence with
the current do-nothing behavior I've missed?


I'm not sure, but it feels odd if poll_start is not the reverse value of poll_stop.

Thanks


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