From: Jason Wang <jasowang@redhat.com>
To: Eugenio Perez Martin <eperezma@redhat.com>
Cc: Parav Pandit <parav@mellanox.com>,
Juan Quintela <quintela@redhat.com>,
Markus Armbruster <armbru@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
qemu-level <qemu-devel@nongnu.org>,
virtualization <virtualization@lists.linux-foundation.org>,
Harpreet Singh Anand <hanand@xilinx.com>,
Xiao W Wang <xiao.w.wang@intel.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
Eli Cohen <eli@mellanox.com>, Eric Blake <eblake@redhat.com>,
Stefano Garzarella <sgarzare@redhat.com>
Subject: Re: [RFC PATCH v4 20/20] vdpa: Add custom IOTLB translations to SVQ
Date: Fri, 15 Oct 2021 15:37:00 +0800 [thread overview]
Message-ID: <CACGkMEuhseBMckdzeGf-bCtyXKEKNNyCaR0LEeELTXhKWxxmwQ@mail.gmail.com> (raw)
In-Reply-To: <CAJaqyWdEGWFNrxqKxRya=ybRiP0wTZ0aPksBBeOe9KOjOmUnqA@mail.gmail.com>
On Fri, Oct 15, 2021 at 3:28 PM Eugenio Perez Martin
<eperezma@redhat.com> wrote:
>
> On Wed, Oct 13, 2021 at 7:34 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> >
> > 在 2021/10/1 下午3:06, Eugenio Pérez 写道:
> > > Use translations added in VhostIOVATree in SVQ.
> > >
> > > Now every element needs to store the previous address also, so VirtQueue
> > > can consume the elements properly. This adds a little overhead per VQ
> > > element, having to allocate more memory to stash them. As a possible
> > > optimization, this allocation could be avoided if the descriptor is not
> > > a chain but a single one, but this is left undone.
> > >
> > > TODO: iova range should be queried before, and add logic to fail when
> > > GPA is outside of its range and memory listener or svq add it.
> > >
> > > Signed-off-by: Eugenio Pérez<eperezma@redhat.com>
> > > ---
> > > hw/virtio/vhost-shadow-virtqueue.h | 4 +-
> > > hw/virtio/vhost-shadow-virtqueue.c | 130 ++++++++++++++++++++++++-----
> > > hw/virtio/vhost-vdpa.c | 40 ++++++++-
> > > hw/virtio/trace-events | 1 +
> > > 4 files changed, 152 insertions(+), 23 deletions(-)
> >
> >
> > Think hard about the whole logic. This is safe since qemu memory map
> > will fail if guest submits a invalidate IOVA.
> >
>
> Can you expand on this? What you mean is that VirtQueue already
> protects SVQ code if the guest sets an invalid buffer address (GPA),
> isn't it?
Yes.
>
> > Then I wonder if we do something much more simpler:
> >
> > 1) Using qemu VA as IOVA but only maps the VA that belongs to guest
> > 2) Then we don't need any IOVA tree here, what we need is to just map
> > vring and use qemu VA without any translation
> >
>
> That would be great, but either qemu's SVQ vring or guest translated
> buffers address (in qemu VA form) were already in high addresses,
> outside of the device's iova range (in my test).
You're right. I miss that and that's why we need e.g iova tree and allocator.
What I proposed only makes sense when shared virtual memory (SVA) is
implemented. In the case of SVA, the valid iova range should be the
full VA range.
>
> I didn't try remapping tricks to make them fit in the range, but I
> think it does complicate the solution relatively fast if there was
> already memory in that range owned by qemu before enabling SVQ:
>
> * Guest memory must be contiguous in VA address space, but it "must"
> support hotplug/unplug (although vDPA currently pins it). Hotplug
> memory could always overlap with SVQ vring, so we would need to move
> it.
> * Duplicating mapped memory for writing? (Not sure if guest memory is
> actually movable in qemu).
> * Indirect descriptors will need to allocate and free memory more or
> less frequently, increasing the possibility of overlapping.
I'm not sure I get the problem, but overlapping is not an issue since
we're using VA.
>
> If we can move guest memory,
I'm not sure we can do this or it looks very tricky.
> however, I can see how we can track it in
> a tree *but* mark when the tree is 1:1 with qemu's VA, so buffers
> forwarding does not take the translation penalty. When guest memory
> cannot be map 1:1, we can resort to tree, and come back to 1:1
> translation if the offending tree node(s) get deleted.
>
> However I think this puts the solution a little bit farther than
> "starting simple" :).
>
> Does it make sense?
Yes. So I think I will review the IOVA tree codes and get back to you.
THanks
>
> Thanks!
>
> > Thanks
> >
>
next prev parent reply other threads:[~2021-10-15 7:38 UTC|newest]
Thread overview: 90+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-01 7:05 [RFC PATCH v4 00/20] vDPA shadow virtqueue Eugenio Pérez
2021-10-01 7:05 ` [RFC PATCH v4 01/20] virtio: Add VIRTIO_F_QUEUE_STATE Eugenio Pérez
2021-10-01 7:05 ` [RFC PATCH v4 02/20] virtio-net: Honor VIRTIO_CONFIG_S_DEVICE_STOPPED Eugenio Pérez
2021-10-01 7:05 ` [RFC PATCH v4 03/20] virtio: Add virtio_queue_is_host_notifier_enabled Eugenio Pérez
2021-10-01 7:05 ` [RFC PATCH v4 04/20] vhost: Make vhost_virtqueue_{start,stop} public Eugenio Pérez
2021-10-01 7:05 ` [RFC PATCH v4 05/20] vhost: Add x-vhost-enable-shadow-vq qmp Eugenio Pérez
2021-10-12 5:18 ` Markus Armbruster
2021-10-12 13:08 ` Eugenio Perez Martin
2021-10-12 13:45 ` Markus Armbruster
2021-10-14 12:01 ` Eugenio Perez Martin
2021-10-01 7:05 ` [RFC PATCH v4 06/20] vhost: Add VhostShadowVirtqueue Eugenio Pérez
2021-10-01 7:05 ` [RFC PATCH v4 07/20] vdpa: Register vdpa devices in a list Eugenio Pérez
2021-10-01 7:05 ` [RFC PATCH v4 08/20] vhost: Route guest->host notification through shadow virtqueue Eugenio Pérez
2021-10-12 5:19 ` Markus Armbruster
2021-10-12 13:09 ` Eugenio Perez Martin
2021-10-13 3:27 ` Jason Wang
2021-10-14 12:00 ` Eugenio Perez Martin
2021-10-15 3:45 ` Jason Wang
2021-10-15 9:08 ` Eugenio Perez Martin
2021-10-15 18:21 ` Eugenio Perez Martin
2021-10-01 7:05 ` [RFC PATCH v4 09/20] vdpa: Save call_fd in vhost-vdpa Eugenio Pérez
2021-10-13 3:43 ` Jason Wang
2021-10-14 12:11 ` Eugenio Perez Martin
2021-10-01 7:05 ` [RFC PATCH v4 10/20] vhost-vdpa: Take into account SVQ in vhost_vdpa_set_vring_call Eugenio Pérez
2021-10-13 3:43 ` Jason Wang
2021-10-14 12:18 ` Eugenio Perez Martin
2021-10-01 7:05 ` [RFC PATCH v4 11/20] vhost: Route host->guest notification through shadow virtqueue Eugenio Pérez
2021-10-13 3:47 ` Jason Wang
2021-10-14 16:39 ` Eugenio Perez Martin
2021-10-15 4:42 ` Jason Wang
2021-10-19 8:39 ` Eugenio Perez Martin
2021-10-20 2:01 ` Jason Wang
2021-10-20 6:36 ` Eugenio Perez Martin
2021-10-13 3:49 ` Jason Wang
2021-10-14 15:58 ` Eugenio Perez Martin
2021-10-15 4:24 ` Jason Wang
2021-10-01 7:05 ` [RFC PATCH v4 12/20] virtio: Add vhost_shadow_vq_get_vring_addr Eugenio Pérez
2021-10-13 3:54 ` Jason Wang
2021-10-14 14:39 ` Eugenio Perez Martin
2021-10-01 7:05 ` [RFC PATCH v4 13/20] vdpa: Save host and guest features Eugenio Pérez
2021-10-13 3:56 ` Jason Wang
2021-10-14 15:03 ` Eugenio Perez Martin
2021-10-01 7:05 ` [RFC PATCH v4 14/20] vhost: Add vhost_svq_valid_device_features to shadow vq Eugenio Pérez
2021-10-01 7:05 ` [RFC PATCH v4 15/20] vhost: Shadow virtqueue buffers forwarding Eugenio Pérez
2021-10-12 5:21 ` Markus Armbruster
2021-10-12 13:28 ` Eugenio Perez Martin
2021-10-12 13:48 ` Markus Armbruster
2021-10-14 15:04 ` Eugenio Perez Martin
2021-10-13 4:31 ` Jason Wang
2021-10-14 17:56 ` Eugenio Perez Martin
2021-10-15 4:23 ` Jason Wang
2021-10-15 9:33 ` Eugenio Perez Martin
2021-10-01 7:05 ` [RFC PATCH v4 16/20] vhost: Check for device VRING_USED_F_NO_NOTIFY at shadow virtqueue kick Eugenio Pérez
2021-10-13 4:35 ` Jason Wang
2021-10-15 6:17 ` Eugenio Perez Martin
2021-10-01 7:06 ` [RFC PATCH v4 17/20] vhost: Use VRING_AVAIL_F_NO_INTERRUPT at device call on shadow virtqueue Eugenio Pérez
2021-10-13 4:36 ` Jason Wang
2021-10-15 6:22 ` Eugenio Perez Martin
2021-10-01 7:06 ` [RFC PATCH v4 18/20] vhost: Add VhostIOVATree Eugenio Pérez
2021-10-19 8:32 ` Jason Wang
2021-10-19 9:22 ` Jason Wang
2021-10-20 7:54 ` Eugenio Perez Martin
2021-10-20 9:01 ` Jason Wang
2021-10-20 12:06 ` Eugenio Perez Martin
2021-10-21 2:34 ` Jason Wang
2021-10-21 7:03 ` Eugenio Perez Martin
2021-10-21 8:12 ` Jason Wang
2021-10-21 14:33 ` Eugenio Perez Martin
2021-10-26 4:29 ` Jason Wang
2021-10-20 7:36 ` Eugenio Perez Martin
2021-10-01 7:06 ` [RFC PATCH v4 19/20] vhost: Use a tree to store memory mappings Eugenio Pérez
2021-10-01 7:06 ` [RFC PATCH v4 20/20] vdpa: Add custom IOTLB translations to SVQ Eugenio Pérez
2021-10-13 5:34 ` Jason Wang
2021-10-15 7:27 ` Eugenio Perez Martin
2021-10-15 7:37 ` Jason Wang [this message]
2021-10-15 8:20 ` Eugenio Perez Martin
2021-10-15 8:37 ` Jason Wang
2021-10-15 9:14 ` Eugenio Perez Martin
2021-10-19 9:24 ` Jason Wang
2021-10-19 10:28 ` Eugenio Perez Martin
2021-10-20 2:02 ` Jason Wang
2021-10-20 2:07 ` Jason Wang
2021-10-20 6:51 ` Eugenio Perez Martin
2021-10-20 9:03 ` Jason Wang
2021-10-20 11:56 ` Eugenio Perez Martin
2021-10-21 2:38 ` Jason Wang
2021-10-26 4:32 ` Jason Wang
2021-10-12 3:59 ` [RFC PATCH v4 00/20] vDPA shadow virtqueue Jason Wang
2021-10-12 4:06 ` Jason Wang
2021-10-12 9:09 ` Eugenio Perez Martin
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