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Date: Tue, 21 Apr 2020 10:27:27 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>,
Richard Earnshaw <Richard.Earnshaw@....com>,
Sudeep Dutt <sudeep.dutt@...el.com>,
Ashutosh Dixit <ashutosh.dixit@...el.com>,
Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v4] vhost: disable for OABI
On 2020/4/20 下午10:34, Michael S. Tsirkin wrote:
> 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@...nel.org>
> Suggested-by: Richard Earnshaw <Richard.Earnshaw@....com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>
> changes from v3:
> update commit log clarifying the motivation and that
> it's a temporary fix.
>
> suggested by Christoph Hellwig
>
> drivers/misc/mic/Kconfig | 2 +-
> drivers/net/caif/Kconfig | 2 +-
> drivers/vdpa/Kconfig | 2 +-
> drivers/vhost/Kconfig | 17 +++++++++++++----
> 4 files changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/misc/mic/Kconfig b/drivers/misc/mic/Kconfig
> index 8f201d019f5a..3bfe72c59864 100644
> --- a/drivers/misc/mic/Kconfig
> +++ b/drivers/misc/mic/Kconfig
> @@ -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
> diff --git a/drivers/net/caif/Kconfig b/drivers/net/caif/Kconfig
> index 9db0570c5beb..661c25eb1c46 100644
> --- a/drivers/net/caif/Kconfig
> +++ b/drivers/net/caif/Kconfig
> @@ -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
> diff --git a/drivers/vdpa/Kconfig b/drivers/vdpa/Kconfig
> index 3e1ceb8e9f2b..e8140065c8a5 100644
> --- a/drivers/vdpa/Kconfig
> +++ b/drivers/vdpa/Kconfig
> @@ -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
> 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
Acked-by: Jason Wang <jasowang@...hat.com>
Thanks
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