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d085eb8ce7
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>
101 lines
2.8 KiB
Plaintext
101 lines
2.8 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0-only
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config VHOST_IOTLB
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tristate
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help
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Generic IOTLB implementation for vhost and vringh.
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This option is selected by any driver which needs to support
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an IOMMU in software.
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config VHOST_RING
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tristate
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select VHOST_IOTLB
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help
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This option is selected by any driver which needs to access
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the host side of a virtio ring.
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config VHOST_DPN
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bool
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depends on !ARM || AEABI
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default y
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help
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Anything selecting VHOST or VHOST_RING must depend on VHOST_DPN.
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This excludes the deprecated ARM ABI since that forces a 4 byte
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alignment on all structs - incompatible with virtio spec requirements.
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config VHOST
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tristate
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select VHOST_IOTLB
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help
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This option is selected by any driver which needs to access
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the core of vhost.
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menuconfig VHOST_MENU
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bool "VHOST drivers"
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default y
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if VHOST_MENU
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config VHOST_NET
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tristate "Host kernel accelerator for virtio net"
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depends on NET && EVENTFD && (TUN || !TUN) && (TAP || !TAP) && VHOST_DPN
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select VHOST
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---help---
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This kernel module can be loaded in host kernel to accelerate
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guest networking with virtio_net. Not to be confused with virtio_net
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module itself which needs to be loaded in guest kernel.
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To compile this driver as a module, choose M here: the module will
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be called vhost_net.
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config VHOST_SCSI
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tristate "VHOST_SCSI TCM fabric driver"
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depends on TARGET_CORE && EVENTFD && VHOST_DPN
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select VHOST
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default n
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---help---
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Say M here to enable the vhost_scsi TCM fabric module
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for use with virtio-scsi guests
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config VHOST_VSOCK
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tristate "vhost virtio-vsock driver"
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depends on VSOCKETS && EVENTFD && VHOST_DPN
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select VHOST
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select VIRTIO_VSOCKETS_COMMON
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default n
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---help---
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This kernel module can be loaded in the host kernel to provide AF_VSOCK
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sockets for communicating with guests. The guests must have the
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virtio_transport.ko driver loaded to use the virtio-vsock device.
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To compile this driver as a module, choose M here: the module will be called
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vhost_vsock.
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config VHOST_VDPA
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tristate "Vhost driver for vDPA-based backend"
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depends on EVENTFD && VHOST_DPN
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select VHOST
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depends on VDPA
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help
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This kernel module can be loaded in host kernel to accelerate
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guest virtio devices with the vDPA-based backends.
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To compile this driver as a module, choose M here: the module
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will be called vhost_vdpa.
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config VHOST_CROSS_ENDIAN_LEGACY
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bool "Cross-endian support for vhost"
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default n
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---help---
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This option allows vhost to support guests with a different byte
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ordering from host while using legacy virtio.
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Userspace programs can control the feature using the
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VHOST_SET_VRING_ENDIAN and VHOST_GET_VRING_ENDIAN ioctls.
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This is only useful on a few platforms (ppc64 and arm64). Since it
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adds some overhead, it is disabled by default.
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If unsure, say "N".
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endif
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