VirtioLib provides an API for simple, synchronous (request/response-style)
virtio communication. The guest driver builds one descriptor chain, link
for link, with VirtioPrepare() and VirtioAppendDesc(), then submits the
chain, and awaits the processing, with VirtioFlush().
The descriptor chain is always built at the beginning of the descriptor
area, with the head descriptor having descriptor index 0.
In order to submit the descriptor chain to the host, the guest always
pushes a new "available element" to the Available Ring, in genuine
queue-like fashion, with the new element referencing the head descriptor
(which always has index 0, see above).
In turn, after processing, the host always pushes a new "used element" to
the Used Ring, in genuine queue-like fashion, with the new element
referencing the head descriptor of the chain that was just processed. The
same element also reports the number of bytes that the host wrote,
consecutively across the host-writeable buffers that were linked by the
descriptors.
(See "OvmfPkg/VirtioNetDxe/TechNotes.txt" for a diagram about the
descriptor area and the rings.)
Because at most one descriptor chain can be in flight with VirtioLib at
any time,
- the Available Ring and the Used Ring proceed in lock-step,
- and the head descriptor that the new "available" and "used" elements can
ever reference has index 0.
Based on the above, we can modify VirtioFlush() to return the number of
bytes written by the host across the descriptor chain. The virtio-block
and virtio-scsi drivers don't care (they have other ways to parse the data
produced by the host), while the virtio-net driver doesn't use
VirtioFlush() at all (it employs VirtioLib only to set up its rings).
However, the virtio entropy device, to be covered in the upcoming
patches, reports the amount of randomness produced by the host only
through this quantity.
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
These functions did not provide much more than the new protocol functions
VIRTIO_DEVICE_PROTOCOL.ReadDevice() / VIRTIO_DEVICE_PROTOCOL.WriteDevice().
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14968 6f19259b-4bc3-4df7-8a09-765794883524
This change replaces the accesses to the PCI bus from the Block, Scsi and Net drivers by
the use of the new VIRTIO_DEVICE_PROTOCOL protocol that abstracts the transport layer.
It means these drivers can be used on PCI and MMIO transport layer.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
v5:
- VirtioFlush(): update comment block in VirtioLib.[hc]; error code is
propagated from VirtIo->SetQueueNotify().
- VirtioBlkInit(): jump to Failed label if SetPageSize() fails
- VirtioBlkInit(): fixup comment, and add error handling, near
SetQueueNum() call
- VirtioBlkDriverBindingStart(): remove redundant (always false) check for
a subsystem device ID different from VIRTIO_SUBSYSTEM_BLOCK_DEVICE;
VirtioBlkDriverBindingSupported() handles it already
- VirtioNetGetFeatures(): update stale comment block
- VirtioNetGetFeatures(): retrieve MAC address byte for byte (open-coded
loop)
- VirtioNetDriverBindingStart(): remove redundant (always false) check for
a subsystem device ID different from VIRTIO_SUBSYSTEM_NETWORK_CARD;
VirtioNetDriverBindingSupported() handles it already
- VirtioNetInitRing(): call SetQueueNum() and SetQueueAlign() for proper
MMIO operation
- VirtioNetInitialize(): fix destination error label for when
SetPageSize() fails
- VirtioScsi.c: fix comment block of VIRTIO_CFG_WRITE()/VIRTIO_CFG_READ()
- VirtioScsiInit(): fix destination error label for when SetPageSize()
fails
- VirtioScsiInit(): call SetQueueNum() and SetQueueAlign() for proper MMIO
operation
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14966 6f19259b-4bc3-4df7-8a09-765794883524
The descriptor table (also known as "queue") consists of descriptors. (The
corresponding type in the code is VRING_DESC.)
An individual descriptor describes a contiguous buffer, to be transferred
uni-directionally between host and guest.
Several descriptors in the descriptor table can be linked into a
descriptor chain, specifying a bi-directional scatter-gather transfer
between host and guest. Such a descriptor chain is also known as "virtio
request".
(The descriptor table can host sereval descriptor chains (in-flight virtio
requests) in parallel, but the OVMF driver supports at most one chain, at
any point in time.)
The first descriptor in any descriptor chain is called "head descriptor".
In order to submit a number of parallel requests (= a set of independent
descriptor chains) from the guest to the host, the guest must put *only*
the head descriptor of each separate chain onto the Available Ring.
VirtioLib currently places the head of its one descriptor chain onto the
Available Ring repeatedly, once for each single (head *or* dependent)
descriptor in said descriptor chain. If the descriptor chain comprises N
descriptors, this error amounts to submitting the same entire chain N
times in parallel.
Available Ring Descriptor table
Ptr to head ----> Desc#0 (head of chain)
Ptr to head --/ Desc#1 (next in same chain)
... / ...
Ptr to head / Desc#(N-1) (last in same chain)
Anatomy of a single virtio-blk READ request (a descriptor chain with three
descriptors):
virtio-blk request header, prepared by guest:
VirtioAppendDesc PhysAddr=3FBC6050 Size=16 Flags=1 Head=1232 Next=1232
payload to be filled in by host:
VirtioAppendDesc PhysAddr=3B934C00 Size=32768 Flags=3 Head=1232 Next=1233
host status, to be filled in by host:
VirtioAppendDesc PhysAddr=3FBC604F Size=1 Flags=2 Head=1232 Next=1234
Processing on the host side -- the descriptor chain is processed three
times in parallel (its head is available to virtqueue_pop() thrice); the
same chain is submitted/collected separately to/from AIO three times:
virtio_queue_notify vdev VDEV vq VQ#0
virtqueue_pop vq VQ#0 elem EL#0 in_num 2 out_num 1
bdrv_aio_readv bs BDRV sector_num 585792 nb_sectors 64 opaque REQ#0
virtqueue_pop vq VQ#0 elem EL#1 in_num 2 out_num 1
bdrv_aio_readv bs BDRV sector_num 585792 nb_sectors 64 opaque REQ#1
virtqueue_pop vq VQ#0 elem EL#2 in_num 2 out_num 1
bdrv_aio_readv bs BDRV sector_num 585792 nb_sectors 64 opaque REQ#2
virtio_blk_rw_complete req REQ#0 ret 0
virtio_blk_req_complete req REQ#0 status 0
virtio_blk_rw_complete req REQ#1 ret 0
virtio_blk_req_complete req REQ#1 status 0
virtio_blk_rw_complete req REQ#2 ret 0
virtio_blk_req_complete req REQ#2 status 0
On my Thinkpad T510 laptop with RHEL-6 as host, this probably leads to
simultaneous DMA transfers targeting the same RAM area. Even though the
source of each transfer is identical, the data is corrupted in the
destination buffer -- the CRC32 calculated over the buffer varies, even
though the origin of the transfers is the same, never rewritten LBA.
SynchronousRequest Lba=585792 BufSiz=32768 ReqIsWrite=0 Crc32=BF68A44D
The problem is invisible on my HP Z400 workstation.
Fix the request submission by:
- building the only one descriptor chain supported by VirtioLib always at
the beginning of the descriptor table,
- ensuring the head descriptor of this chain is put on the Available Ring
only once,
- requesting the virtio spec's language to be cleaned up
<http://lists.linuxfoundation.org/pipermail/virtualization/2013-April/024032.html>.
Available Ring Descriptor table
Ptr to head ----> Desc#0 (head of chain)
Desc#1 (next in same chain)
...
Desc#(N-1) (last in same chain)
VirtioAppendDesc PhysAddr=3FBC6040 Size=16 Flags=1 Head=0 Next=0
VirtioAppendDesc PhysAddr=3B934C00 Size=32768 Flags=3 Head=0 Next=1
VirtioAppendDesc PhysAddr=3FBC603F Size=1 Flags=2 Head=0 Next=2
virtio_queue_notify vdev VDEV vq VQ#0
virtqueue_pop vq VQ#0 elem EL#0 in_num 2 out_num 1
bdrv_aio_readv bs BDRV sector_num 585792 nb_sectors 64 opaque REQ#0
virtio_blk_rw_complete req REQ#0 ret 0
virtio_blk_req_complete req REQ#0 status 0
SynchronousRequest Lba=585792 BufSiz=32768 ReqIsWrite=0 Crc32=1EEB2B07
(The Crc32 was double-checked with edk2's and Linux's guest IDE driver.)
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@14356 6f19259b-4bc3-4df7-8a09-765794883524
AppendDesc() should have a prefix implying its containing library,
VirtioLib. Update its sole client VirtioBlkDxe.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13843 6f19259b-4bc3-4df7-8a09-765794883524
Introduce a new library called VirtioLib, for now only collecting the
following reusable functions with as little changes as possible:
- VirtioWrite()
- VirtioRead()
- VirtioRingInit()
- VirtioRingUninit()
- AppendDesc()
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13842 6f19259b-4bc3-4df7-8a09-765794883524
Laszlo Ersek
Olivier Martin
jljusten