VDUSE (vDPA Device in Userspace) is a framework to support
implementing software-emulated vDPA devices in userspace. This
document is intended to clarify the VDUSE design and usage.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>

This VDUSE driver enables implementing software-emulated vDPA
devices in userspace. The vDPA device is created by
ioctl(VDUSE_CREATE_DEV) on /dev/vduse/control. Then a char device
interface (/dev/vduse/$NAME) is exported to userspace for device
emulation.

In order to make the device emulation more secure, the device's
control path is handled in kernel. A message mechnism is introduced
to forward some dataplane related control messages to userspace.

And in the data path, the DMA buffer will be mapped into userspace
address space through different ways depending on the vDPA bus to
which the vDPA device is attached. In virtio-vdpa case, the MMU-based
IOMMU driver is used to achieve that. And in vhost-vdpa case, the
DMA buffer is reside in a userspace memory region which can be shared
to the VDUSE userspace processs via transferring the shmfd.

For more details on VDUSE design and usage, please see the follow-on
Documentation commit.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>

This implements an MMU-based IOMMU driver to support mapping
kernel dma buffer into userspace. The basic idea behind it is
treating MMU (VA->PA) as IOMMU (IOVA->PA). The driver will set
up MMU mapping instead of IOMMU mapping for the DMA transfer so
that the userspace process is able to use its virtual address to
access the dma buffer in kernel.

And to avoid security issue, a bounce-buffering mechanism is
introduced to prevent userspace accessing the original buffer
directly.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Acked-by: Jason Wang <jasowang@redhat.com>

This patch introduces an attribute for vDPA device to indicate
whether virtual address can be used. If vDPA device driver set
it, vhost-vdpa bus driver will not pin user page and transfer
userspace virtual address instead of physical address during
DMA mapping. And corresponding vma->vm_file and offset will be
also passed as an opaque pointer.

Suggested-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Acked-by: Jason Wang <jasowang@redhat.com>

The upcoming patch is going to support VA mapping/unmapping.
So let's factor out the logic of PA mapping/unmapping firstly
to make the code more readable.

Suggested-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Acked-by: Jason Wang <jasowang@redhat.com>

Add an opaque pointer for DMA mapping.

Suggested-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Acked-by: Jason Wang <jasowang@redhat.com>

Add an opaque pointer for vhost IOTLB. And introduce
vhost_iotlb_add_range_ctx() to accept it.

Suggested-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Acked-by: Jason Wang <jasowang@redhat.com>

The device reset may fail in virtio-vdpa case now, so add checks to
its return value and fail the register_virtio_device().

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>

The vpda_reset() may fail now. This adds check to its return
value and fail the virtio_vdpa_reset().

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>

This adds a return value to reset function so that we can
handle the reset failure later. No functional changes.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>

We don't need to set FAILED status bit on device index allocation
failure since the device initialization hasn't been started yet.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>

The vdpa_reset() may fail now. This adds check to its return
value and fail the vhost_vdpa_open().

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>

Re-read the device status to ensure it's set to zero during
resetting. Otherwise, fail the vhost_vdpa_set_status() after timeout.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>

Re-read the device status to ensure it's set to zero during
resetting. Otherwise, fail the vdpa_reset() after timeout.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>

Use tabs to indent the code instead of spaces.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>

Export receive_fd() so that some modules can use
it to pass file descriptor between processes without
missing any security stuffs.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>

Export alloc_iova_fast() and free_iova_fast() so that
some modules can use it to improve iova allocation efficiency.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>

Let's handle unplug in Big Block Mode similar to Sub Block Mode --
prioritize memory blocks onlined to ZONE_MOVABLE.

We won't care further about big blocks with mixed zones, as it's
rather a corner case that won't matter in practice.

Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20210602185720.31821-8-david@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Let's simplify high-level big block selection when unplugging in
Big Block Mode.

Combine handling of offline and online blocks. We can get rid of
virtio_mem_bbm_bb_is_offline() and simply use
virtio_mem_bbm_offline_remove_and_unplug_bb(), as that already tolerates
offline parts.

We can race with concurrent onlining/offlining either way, so we don;t
have to be super correct by failing if an offline big block we'd like to
unplug just got (partially) onlined.

Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20210602185720.31821-7-david@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Until now, memory provided by a single virtio-mem device was usually
either onlined completely to ZONE_MOVABLE (online_movable) or to
ZONE_NORMAL (online_kernel); however, that will change in the future.

There are two reasons why we want to track to which zone a memory blocks
belongs to and prioritize ZONE_MOVABLE blocks:

1) Memory managed by ZONE_MOVABLE can more likely get unplugged, therefore,
   resulting in a faster memory hotunplug process. Further, we can more
   reliably unplug and remove complete memory blocks, removing metadata
   allocated for the whole memory block.

2) We want to avoid corner cases where unplugging with the current scheme
   (highest to lowest address) could result in accidential zone imbalances,
   whereby we remove too much ZONE_NORMAL memory for ZONE_MOVABLE memory
   of the same device.

Let's track the zone via memory block states and try unplug from
ZONE_MOVABLE first. Rename VIRTIO_MEM_SBM_MB_ONLINE* to
VIRTIO_MEM_SBM_MB_KERNEL* to avoid even longer state names.

In commit 27f8527 ("virtio-mem: don't special-case ZONE_MOVABLE"),
we removed slightly similar tracking for fully plugged memory blocks to
support unplugging from ZONE_MOVABLE at all -- as we didn't allow partially
plugged memory blocks in ZONE_MOVABLE before that. That commit already
mentioned "In the future, we might want to remember the zone again and use
the information when (un)plugging memory."

Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20210602185720.31821-6-david@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Let's simplify by introducing a new virtio_mem_sbm_unplug_any_sb(),
similar to virtio_mem_sbm_plug_any_sb(), to simplify high-level memory
block selection when unplugging in Sub Block Mode.

Rename existing virtio_mem_sbm_unplug_any_sb() to
virtio_mem_sbm_unplug_any_sb_raw().

The only change is that we now temporarily unlock the hotplug mutex around
cond_resched() when processing offline memory blocks, which doesn't
make a real difference as we already have to temporarily unlock in
virtio_mem_sbm_unplug_any_sb_offline() when removing a memory block.

Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20210602185720.31821-5-david@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Let's simplify high-level memory block selection when plugging in Sub
Block Mode.

No need for two separate loops when selecting memory blocks for plugging
memory. Avoid passing the "online" state by simply obtaining the state
in virtio_mem_sbm_plug_any_sb().

Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20210602185720.31821-4-david@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Let's use page_zonenum() instead of zone_idx(page_zone()).

Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20210602185720.31821-3-david@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

We are reading a Big Block Mode value while in Sub Block Mode
when initializing. Fortunately, vm->bbm.bb_size maps to some counter
in the vm->sbm.mb_count array, which is 0 at that point in time.

No harm done; still, this was unintended and is not future-proof.

Fixes: 4ba50cd ("virtio-mem: Big Block Mode (BBM) memory hotplug")
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20210602185720.31821-2-david@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Clear the available index as part of the initialization process to
clear and values that might be left from previous usage of the device.
For example, if the device was previously used by vhost_vdpa and now
probed by vhost_vdpa, you want to start with indices.

Fixes: c043b4a ("virtio: introduce a vDPA based transport")
Signed-off-by: Eli Cohen <elic@nvidia.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210602021536.39525-5-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>

We used to fail the set_vq_state() since it was not supported yet by
the virtio spec. But if the bus tries to set the state which is equal
to the device initial state after reset, we can let it go.

This is a must for virtio_vdpa() to set vq state during probe which is
required for some vDPA parents.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210602021536.39525-4-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>

This patch introduce a helper to get driver/guest features from the
device.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210602021536.39525-3-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>

This patch extends the vdpa_vq_state to support packed virtqueue
state which is basically the device/driver ring wrap counters and the
avail and used index. This will be used for the virito-vdpa support
for the packed virtqueue and the future vhost/vhost-vdpa support for
the packed virtqueue.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210602021536.39525-2-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>

For split virtqueue, we used to depend on the address, length and
flags stored in the descriptor ring for DMA unmapping. This is unsafe
for the case since the device can manipulate the behavior of virtio
driver, IOMMU drivers and swiotlb.

For safety, maintain the DMA address, DMA length, descriptor flags and
next filed of the non indirect descriptors in vring_desc_state_extra
when DMA API is used for virtio as we did for packed virtqueue and use
those metadata for performing DMA operations. Indirect descriptors
should be safe since they are using streaming mappings.

With this the descriptor ring is write only form the view of the
driver.

This slight increase the footprint of the drive but it's not noticed
through pktgen (64B) test and netperf test in the case of virtio-net.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210604055350.58753-8-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Using error label for unwind in __vring_new_virtqueue. This is useful
for future refacotring.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210604055350.58753-7-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

This patch introduces a helper for storing descriptor in the
descriptor table for split virtqueue.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210604055350.58753-6-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

We should not depend on the DMA address, length and flag of descriptor
table since they could be wrote with arbitrary value by the device. So
this patch switches to use the stored one in desc_extra.

Note that the indirect descriptors are fine since they are read-only
streaming mappings.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210604055350.58753-5-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

A helper is introduced for the logic of allocating the descriptor
extra data. This will be reused by split virtqueue.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210604055350.58753-4-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Rename vring_desc_extra_packed to vring_desc_extra since the structure
are pretty generic which could be reused by split virtqueue as well.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210604055350.58753-3-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

This patch moves next from vring_desc_state_packed to
vring_desc_desc_extra_packed. This makes it simpler to let extra state
to be reused by split virtqueue.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210604055350.58753-2-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>