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Tsirkin" , qemu-level , Markus Armbruster , Harpreet Singh Anand , Xiao W Wang , Stefan Hajnoczi , Eli Cohen , virtualization@lists.linux-foundation.org, Michael Lilja , Jim Harford , Stefano Garzarella Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Feb 4, 2021 at 4:14 AM Jason Wang wrote: > > > On 2021/2/2 =E4=B8=8B=E5=8D=886:17, Eugenio Perez Martin wrote: > > On Tue, Feb 2, 2021 at 4:31 AM Jason Wang wrote: > >> > >> On 2021/2/1 =E4=B8=8B=E5=8D=884:28, Eugenio Perez Martin wrote: > >>> On Mon, Feb 1, 2021 at 7:13 AM Jason Wang wrote= : > >>>> On 2021/1/30 =E4=B8=8A=E5=8D=884:54, Eugenio P=C3=A9rez wrote: > >>>>> Signed-off-by: Eugenio P=C3=A9rez > >>>>> --- > >>>>> include/hw/virtio/vhost.h | 1 + > >>>>> hw/virtio/vhost.c | 17 +++++++++++++++++ > >>>>> 2 files changed, 18 insertions(+) > >>>>> > >>>>> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h > >>>>> index 4a8bc75415..fca076e3f0 100644 > >>>>> --- a/include/hw/virtio/vhost.h > >>>>> +++ b/include/hw/virtio/vhost.h > >>>>> @@ -123,6 +123,7 @@ uint64_t vhost_get_features(struct vhost_dev *h= dev, const int *feature_bits, > >>>>> void vhost_ack_features(struct vhost_dev *hdev, const int *feat= ure_bits, > >>>>> uint64_t features); > >>>>> bool vhost_has_free_slot(void); > >>>>> +struct vhost_dev *vhost_dev_from_virtio(const VirtIODevice *vdev); > >>>>> > >>>>> int vhost_net_set_backend(struct vhost_dev *hdev, > >>>>> struct vhost_vring_file *file); > >>>>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > >>>>> index 28c7d78172..8683d507f5 100644 > >>>>> --- a/hw/virtio/vhost.c > >>>>> +++ b/hw/virtio/vhost.c > >>>>> @@ -61,6 +61,23 @@ bool vhost_has_free_slot(void) > >>>>> return slots_limit > used_memslots; > >>>>> } > >>>>> > >>>>> +/* > >>>>> + * Get the vhost device associated to a VirtIO device. > >>>>> + */ > >>>>> +struct vhost_dev *vhost_dev_from_virtio(const VirtIODevice *vdev) > >>>>> +{ > >>>>> + struct vhost_dev *hdev; > >>>>> + > >>>>> + QLIST_FOREACH(hdev, &vhost_devices, entry) { > >>>>> + if (hdev->vdev =3D=3D vdev) { > >>>>> + return hdev; > >>>>> + } > >>>>> + } > >>>>> + > >>>>> + assert(hdev); > >>>>> + return NULL; > >>>>> +} > >>>> I'm not sure this can work in the case of multiqueue. E.g vhost-net > >>>> multiqueue is a N:1 mapping between vhost devics and virtio devices. > >>>> > >>>> Thanks > >>>> > >>> Right. We could add an "vdev vq index" parameter to the function in > >>> this case, but I guess the most reliable way to do this is to add a > >>> vhost_opaque value to VirtQueue, as Stefan proposed in previous RFC. > >> > >> So the question still, it looks like it's easier to hide the shadow > >> virtqueue stuffs at vhost layer instead of expose them to virtio layer= : > >> > >> 1) vhost protocol is stable ABI > >> 2) no need to deal with virtio stuffs which is more complex than vhost > >> > >> Or are there any advantages if we do it at virtio layer? > >> > > As far as I can tell, we will need the virtio layer the moment we > > start copying/translating buffers. > > > > In this series, the virtio dependency can be reduced if qemu does not > > check the used ring _F_NO_NOTIFY flag before writing to irqfd. It > > would enable packed queues and IOMMU immediately, and I think the cost > > should not be so high. In the previous RFC this check was deleted > > later anyway, so I think it was a bad idea to include it from the start= . > > > I am not sure I understand here. For vhost, we can still do anything we > want, e.g accessing guest memory etc. Any blocker that prevent us from > copying/translating buffers? (Note that qemu will propagate memory > mappings to vhost). > There is nothing that forbids us to access directly, but if we don't reuse the virtio layer functionality we would have to duplicate every access function. "Need" was a too strong word maybe :). In other words: for the shadow vq vring exposed for the device, qemu treats it as a driver, and this functionality needs to be added to qemu. But for accessing the guest's one do not reuse virtio.c would be a bad idea in my opinion. > Thanks > > > > > > > > > > > > > >> Thanks > >> > >> > >>> I need to take this into account in qmp_x_vhost_enable_shadow_vq too. > >>> > >>>>> + > >>>>> static void vhost_dev_sync_region(struct vhost_dev *dev, > >>>>> MemoryRegionSection *section, > >>>>> uint64_t mfirst, uint64_t mla= st, > > >