linux-stable/drivers/vhost/Kconfig
Michael S. Tsirkin d085eb8ce7 vhost: disable for OABI
vhost is currently broken on the some ARM configs.

The reason is that the ring element addresses are passed between
components with different alignments assumptions. Thus, if
guest selects a pointer and host then gets and dereferences
it, then alignment assumed by the host's compiler might be
greater than the actual alignment of the pointer.
compiler on the host from assuming pointer is aligned.

This actually triggers on ARM with -mabi=apcs-gnu - which is a
deprecated configuration. With this OABI, compiler assumes that
all structures are 4 byte aligned - which is stronger than
virtio guarantees for available and used rings, which are
merely 2 bytes. Thus a guest without -mabi=apcs-gnu running
on top of host with -mabi=apcs-gnu will be broken.

The correct fix is to force alignment of structures - however
that is an intrusive fix that's best deferred until the next release.

We didn't previously support such ancient systems at all - this surfaced
after vdpa support prompted removing dependency of vhost on
VIRTULIZATION. So for now, let's just add something along the lines of

	depends on !ARM || AEABI

to the virtio Kconfig declaration, and add a comment that it has to do
with struct member alignment.

Note: we can't make VHOST and VHOST_RING themselves have
a dependency since these are selected. Add a new symbol for that.

We should be able to drop this dependency down the road.

Fixes: 20c384f1ea ("vhost: refine vhost and vringh kconfig")
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Suggested-by: Richard Earnshaw <Richard.Earnshaw@arm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2020-04-20 10:19:22 -04:00

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# SPDX-License-Identifier: GPL-2.0-only
config VHOST_IOTLB
tristate
help
Generic IOTLB implementation for vhost and vringh.
This option is selected by any driver which needs to support
an IOMMU in software.
config VHOST_RING
tristate
select VHOST_IOTLB
help
This option is selected by any driver which needs to access
the host side of a virtio ring.
config VHOST_DPN
bool
depends on !ARM || AEABI
default y
help
Anything selecting VHOST or VHOST_RING must depend on VHOST_DPN.
This excludes the deprecated ARM ABI since that forces a 4 byte
alignment on all structs - incompatible with virtio spec requirements.
config VHOST
tristate
select VHOST_IOTLB
help
This option is selected by any driver which needs to access
the core of vhost.
menuconfig VHOST_MENU
bool "VHOST drivers"
default y
if VHOST_MENU
config VHOST_NET
tristate "Host kernel accelerator for virtio net"
depends on NET && EVENTFD && (TUN || !TUN) && (TAP || !TAP) && VHOST_DPN
select VHOST
---help---
This kernel module can be loaded in host kernel to accelerate
guest networking with virtio_net. Not to be confused with virtio_net
module itself which needs to be loaded in guest kernel.
To compile this driver as a module, choose M here: the module will
be called vhost_net.
config VHOST_SCSI
tristate "VHOST_SCSI TCM fabric driver"
depends on TARGET_CORE && EVENTFD && VHOST_DPN
select VHOST
default n
---help---
Say M here to enable the vhost_scsi TCM fabric module
for use with virtio-scsi guests
config VHOST_VSOCK
tristate "vhost virtio-vsock driver"
depends on VSOCKETS && EVENTFD && VHOST_DPN
select VHOST
select VIRTIO_VSOCKETS_COMMON
default n
---help---
This kernel module can be loaded in the host kernel to provide AF_VSOCK
sockets for communicating with guests. The guests must have the
virtio_transport.ko driver loaded to use the virtio-vsock device.
To compile this driver as a module, choose M here: the module will be called
vhost_vsock.
config VHOST_VDPA
tristate "Vhost driver for vDPA-based backend"
depends on EVENTFD && VHOST_DPN
select VHOST
depends on VDPA
help
This kernel module can be loaded in host kernel to accelerate
guest virtio devices with the vDPA-based backends.
To compile this driver as a module, choose M here: the module
will be called vhost_vdpa.
config VHOST_CROSS_ENDIAN_LEGACY
bool "Cross-endian support for vhost"
default n
---help---
This option allows vhost to support guests with a different byte
ordering from host while using legacy virtio.
Userspace programs can control the feature using the
VHOST_SET_VRING_ENDIAN and VHOST_GET_VRING_ENDIAN ioctls.
This is only useful on a few platforms (ppc64 and arm64). Since it
adds some overhead, it is disabled by default.
If unsure, say "N".
endif