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| author | Michael S. Tsirkin <mst@redhat.com> | 2020-04-06 15:12:47 +0300 |
|---|---|---|
| committer | Michael S. Tsirkin <mst@redhat.com> | 2020-04-20 17:19:22 +0300 |
| commit | d085eb8ce727e581abf8145244eaa3339021be2f (patch) | |
| tree | ce3b3b41cb4c7a5eec3c0320a315210bfe5d007f /drivers/vhost | |
| parent | 15064e70909cd8cca092ed6dd888bdbd9fefaae3 (diff) | |
| download | linux-d085eb8ce727e581abf8145244eaa3339021be2f.tar.xz | |
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: 20c384f1ea1a0bc7 ("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>
Diffstat (limited to 'drivers/vhost')
| -rw-r--r-- | drivers/vhost/Kconfig | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig index 2c75d164b827..c4f273793595 100644 --- a/drivers/vhost/Kconfig +++ b/drivers/vhost/Kconfig @@ -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 |