Commit d085eb8c authored by Michael S. Tsirkin's avatar Michael S. Tsirkin
Browse files

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: 20c384f1 ("vhost: refine vhost and vringh kconfig")
Suggested-by: default avatarArd Biesheuvel <ardb@kernel.org>
Suggested-by: default avatarRichard Earnshaw <Richard.Earnshaw@arm.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 15064e70

drivers/misc/mic/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -116,7 +116,7 @@ config MIC_COSM 


config VOP

	tristate "VOP Driver"

	depends on VOP_BUS

	depends on VOP_BUS && VHOST_DPN

	select VHOST_RING

	select VIRTIO

	help

drivers/net/caif/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -50,7 +50,7 @@ config CAIF_HSI 


config CAIF_VIRTIO

	tristate "CAIF virtio transport driver"

	depends on CAIF && HAS_DMA

	depends on CAIF && HAS_DMA && VHOST_DPN

	select VHOST_RING

	select VIRTIO

	select GENERIC_ALLOCATOR

drivers/vdpa/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -10,7 +10,7 @@ if VDPA 


config VDPA_SIM

	tristate "vDPA device simulator"

	depends on RUNTIME_TESTING_MENU && HAS_DMA

	depends on RUNTIME_TESTING_MENU && HAS_DMA && VHOST_DPN

	select VHOST_RING

	default n

	help

drivers/vhost/Kconfig

+13 −4
Original line number Diff line number Diff line
@@ -13,6 +13,15 @@ config VHOST_RING 
	  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
@@ -28,7 +37,7 @@ if VHOST_MENU 


config VHOST_NET

	tristate "Host kernel accelerator for virtio net"

	depends on NET && EVENTFD && (TUN || !TUN) && (TAP || !TAP)

	depends on NET && EVENTFD && (TUN || !TUN) && (TAP || !TAP) && VHOST_DPN

	select VHOST

	---help---

	  This kernel module can be loaded in host kernel to accelerate
@@ -40,7 +49,7 @@ config VHOST_NET 


config VHOST_SCSI

	tristate "VHOST_SCSI TCM fabric driver"

	depends on TARGET_CORE && EVENTFD

	depends on TARGET_CORE && EVENTFD && VHOST_DPN

	select VHOST

	default n

	---help---
@@ -49,7 +58,7 @@ config VHOST_SCSI 


config VHOST_VSOCK

	tristate "vhost virtio-vsock driver"

	depends on VSOCKETS && EVENTFD

	depends on VSOCKETS && EVENTFD && VHOST_DPN

	select VHOST

	select VIRTIO_VSOCKETS_COMMON

	default n
@@ -63,7 +72,7 @@ config VHOST_VSOCK 


config VHOST_VDPA

	tristate "Vhost driver for vDPA-based backend"

	depends on EVENTFD

	depends on EVENTFD && VHOST_DPN

	select VHOST

	depends on VDPA

	help

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