OpenCloudOS-Kernel/drivers/virtio
Halil Pasic 2f9a174f91 virtio: write back F_VERSION_1 before validate
The virtio specification virtio-v1.1-cs01 states: "Transitional devices
MUST detect Legacy drivers by detecting that VIRTIO_F_VERSION_1 has not
been acknowledged by the driver."  This is exactly what QEMU as of 6.1
has done relying solely on VIRTIO_F_VERSION_1 for detecting that.

However, the specification also says: "... the driver MAY read (but MUST
NOT write) the device-specific configuration fields to check that it can
support the device ..." before setting FEATURES_OK.

In that case, any transitional device relying solely on
VIRTIO_F_VERSION_1 for detecting legacy drivers will return data in
legacy format.  In particular, this implies that it is in big endian
format for big endian guests. This naturally confuses the driver which
expects little endian in the modern mode.

It is probably a good idea to amend the spec to clarify that
VIRTIO_F_VERSION_1 can only be relied on after the feature negotiation
is complete. Before validate callback existed, config space was only
read after FEATURES_OK. However, we already have two regressions, so
let's address this here as well.

The regressions affect the VIRTIO_NET_F_MTU feature of virtio-net and
the VIRTIO_BLK_F_BLK_SIZE feature of virtio-blk for BE guests when
virtio 1.0 is used on both sides. The latter renders virtio-blk unusable
with DASD backing, because things simply don't work with the default.
See Fixes tags for relevant commits.

For QEMU, we can work around the issue by writing out the feature bits
with VIRTIO_F_VERSION_1 bit set.  We (ab)use the finalize_features
config op for this. This isn't enough to address all vhost devices since
these do not get the features until FEATURES_OK, however it looks like
the affected devices actually never handled the endianness for legacy
mode correctly, so at least that's not a regression.

No devices except virtio net and virtio blk seem to be affected.

Long term the right thing to do is to fix the hypervisors.

Cc: <stable@vger.kernel.org> #v4.11
Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Fixes: 82e89ea077 ("virtio-blk: Add validation for block size in config space")
Fixes: fe36cbe067 ("virtio_net: clear MTU when out of range")
Reported-by: markver@us.ibm.com
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Link: https://lore.kernel.org/r/20211011053921.1198936-1-pasic@linux.ibm.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2021-10-13 08:35:36 -04:00
..
Kconfig virtio-pci: introduce modern device module 2021-02-23 07:52:58 -05:00
Makefile virtio-pci: introduce modern device module 2021-02-23 07:52:58 -05:00
virtio.c virtio: write back F_VERSION_1 before validate 2021-10-13 08:35:36 -04:00
virtio_balloon.c virtio-balloon: Use virtio_find_vqs() helper 2021-09-06 07:20:56 -04:00
virtio_dma_buf.c virtio: fix build for configs without dma-bufs 2020-08-19 06:43:28 +02:00
virtio_input.c virtio-input: add multi-touch support 2021-02-23 07:52:59 -05:00
virtio_mem.c virtio-mem: use a single dynamic memory group for a single virtio-mem device 2021-09-08 11:50:23 -07:00
virtio_mmio.c virtio-mmio: Use to_virtio_mmio_device() to simply code 2021-03-14 04:37:35 -04:00
virtio_pci_common.c virtio_pci: Support surprise removal of virtio pci device 2021-08-10 11:50:55 -04:00
virtio_pci_common.h virtio-pci: introduce modern device module 2021-02-23 07:52:58 -05:00
virtio_pci_legacy.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 78 2019-05-24 17:37:51 +02:00
virtio_pci_modern.c virtio_pci_modern: __force cast the notify mapping 2021-05-04 04:19:58 -04:00
virtio_pci_modern_dev.c virtio-pci library: introduce vp_modern_get_driver_features() 2021-07-08 07:49:01 -04:00
virtio_ring.c virtio_ring: pull in spinlock header 2021-08-11 06:44:24 -04:00
virtio_vdpa.c virtio_vdpa: reject invalid vq indices 2021-08-11 06:44:23 -04:00