similar to: [PATCH] vhost: relax used address alignment

virtio 1.0 only requires used address to be 4 byte aligned, vhost required 8 bytes (size of vring_used_elem). Fix up vhost to match that. Additionally, while vhost correctly requires 8 byte alignment for log, it's unconnected to used ring: it's a consequence that log has u64 entries. Tweak code to make that clearer. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> ---

virtio 1.0 only requires used address to be 4 byte aligned, vhost required 8 bytes (size of vring_used_elem). Fix up vhost to match that. Additionally, while vhost correctly requires 8 byte alignment for log, it's unconnected to used ring: it's a consequence that log has u64 entries. Tweak code to make that clearer. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> ---

commit 5d9a07b0de512b77bf28d2401e5fe3351f00a240 ("vhost: relax used address alignment") fixed the alignment for the used virtual address, but not for the physical address used for logging. That's a mistake: alignment should clearly be the same for virtual and physical addresses, Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- drivers/vhost/vhost.c | 2 +- 1 file

commit 5d9a07b0de512b77bf28d2401e5fe3351f00a240 ("vhost: relax used address alignment") fixed the alignment for the used virtual address, but not for the physical address used for logging. That's a mistake: alignment should clearly be the same for virtual and physical addresses, Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- drivers/vhost/vhost.c | 2 +- 1 file

The VHOST_VRING_F_LEGACY_BIG_ENDIAN flag informs the kernel that the associated device is big endian. Of course, this only makes sense for legacy virtio devices since modern virtio devices are always little endian. It will be used by the vhost memory accessors to byteswap vring data when we have a legacy device, in case host and guest endianness differ. Signed-off-by: Greg Kurz <gkurz at

The VHOST_VRING_F_LEGACY_BIG_ENDIAN flag informs the kernel that the associated device is big endian. Of course, this only makes sense for legacy virtio devices since modern virtio devices are always little endian. It will be used by the vhost memory accessors to byteswap vring data when we have a legacy device, in case host and guest endianness differ. Signed-off-by: Greg Kurz <gkurz at

With PUBLISH_USED_IDX, guest tells us which used entries it has consumed. This can be used to reduce the number of interrupts: after we write a used entry, if the guest has not yet consumed the previous entry, or if the guest has already consumed the new entry, we do not need to interrupt. This imporves bandwidth by 30% under some workflows. Signed-off-by: Michael S. Tsirkin <mst at

With PUBLISH_USED_IDX, guest tells us which used entries it has consumed. This can be used to reduce the number of interrupts: after we write a used entry, if the guest has not yet consumed the previous entry, or if the guest has already consumed the new entry, we do not need to interrupt. This imporves bandwidth by 30% under some workflows. Signed-off-by: Michael S. Tsirkin <mst at

With PUBLISH_USED_IDX, guest tells us which used entries it has consumed. This can be used to reduce the number of interrupts: after we write a used entry, if the guest has not yet consumed the previous entry, or if the guest has already consumed the new entry, we do not need to interrupt. This imporves bandwidth by 30% under some workflows. Signed-off-by: Michael S. Tsirkin <mst at

With PUBLISH_USED_IDX, guest tells us which used entries it has consumed. This can be used to reduce the number of interrupts: after we write a used entry, if the guest has not yet consumed the previous entry, or if the guest has already consumed the new entry, we do not need to interrupt. This imporves bandwidth by 30% under some workflows. Signed-off-by: Michael S. Tsirkin <mst at

We need to set log when updating flags of used ring, otherwise they may be missed after migration. A helper was introduced to write used_flags back to guest memory and update the log if necessary. Signed-off-by: Jason Wang <jasowang at redhat.com> --- drivers/vhost/vhost.c | 26 ++++++++++++++++++++++---- drivers/vhost/vhost.h | 2 ++ 2 files changed, 24 insertions(+), 4 deletions(-)

We need to set log when updating flags of used ring, otherwise they may be missed after migration. A helper was introduced to write used_flags back to guest memory and update the log if necessary. Signed-off-by: Jason Wang <jasowang at redhat.com> --- drivers/vhost/vhost.c | 26 ++++++++++++++++++++++---- drivers/vhost/vhost.h | 2 ++ 2 files changed, 24 insertions(+), 4 deletions(-)

On 2019/7/3 ??5:13, Tiwei Bie wrote: > Details about this can be found here: > > https://lwn.net/Articles/750770/ > > What's new in this version > ========================== > > A new VFIO device type is introduced - vfio-vhost. This addressed > some comments from here: https://patchwork.ozlabs.org/cover/984763/ > > Below is the updated device interface: >

On biarch kernels, it is not safe to do copy from/to user, even with use_mm, unless we checked the address range with access_ok previously. Implement these checks to enforce safe memory accesses. Reported-by: Al Viro <viro at zeniv.linux.org.uk> Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- drivers/vhost/net.c | 17 ++++++- drivers/vhost/vhost.c | 111

On biarch kernels, it is not safe to do copy from/to user, even with use_mm, unless we checked the address range with access_ok previously. Implement these checks to enforce safe memory accesses. Reported-by: Al Viro <viro at zeniv.linux.org.uk> Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- drivers/vhost/net.c | 17 ++++++- drivers/vhost/vhost.c | 111

From: Alan Cox <alan at linux.intel.com> Subject: [PATCH] vhost: fix warnings on 32 bit systems Fix compiler warning about discarding top 32 bit of data on 32 bit systems, and document that dicarded bits must be 0. Signed-off-by: Alan Cox <alan at linux.intel.com> Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- So I think the below slightly tweaked version of

From: Alan Cox <alan at linux.intel.com> Subject: [PATCH] vhost: fix warnings on 32 bit systems Fix compiler warning about discarding top 32 bit of data on 32 bit systems, and document that dicarded bits must be 0. Signed-off-by: Alan Cox <alan at linux.intel.com> Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- So I think the below slightly tweaked version of

It was noticed that the copy_user() friends that was used to access virtqueue metdata tends to be very expensive for dataplane implementation like vhost since it involves lots of software checks, speculation barrier, hardware feature toggling (e.g SMAP). The extra cost will be more obvious when transferring small packets since the time spent on metadata accessing become more significant. This

On 2018?04?02? 23:23, Tiwei Bie wrote: > This patch introduces a mdev (mediated device) based hardware > vhost backend. This backend is an abstraction of the various > hardware vhost accelerators (potentially any device that uses > virtio ring can be used as a vhost accelerator). Some generic > mdev parent ops are provided for accelerator drivers to support > generating mdev

On Wed, Mar 06, 2019 at 02:18:12AM -0500, Jason Wang wrote: > It was noticed that the copy_user() friends that was used to access > virtqueue metdata tends to be very expensive for dataplane > implementation like vhost since it involves lots of software checks, > speculation barrier, hardware feature toggling (e.g SMAP). The > extra cost will be more obvious when transferring small