Re: [dpdk-dev] [PATCH v2] vhost: enable reply-ack systematically

["Xia, Chenbo" <chenbo.xia@intel.com>]

> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of Maxime Coquelin
> Sent: Thursday, May 28, 2020 5:04 PM
> To: dev@dpdk.org; Ye, Xiaolong <xiaolong.ye@intel.com>;
> amorenoz@redhat.com; david.marchand@redhat.com; thomas@monjalon.net
> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
> Subject: [dpdk-dev] [PATCH v2] vhost: enable reply-ack systematically
> 
> As announced during v20.05 release cycle, this patch makes reply-ack protocol
> feature to be enabled unconditionally.
> 
> This protocol feature makes the communication between the master and the
> slave more robust, avoiding for example possible undefined behaviour with
> VHOST_USER_SET_MEM_TABLE.
> 
> Also, reply-ack support will be required for upcoming VHOST_USER_SET_STATUS
> request.
> 
> Note that this protocol feature was disabled by default because Qemu version
> 2.7.0 to 2.9.0 had a bug causing a deadlock when reply-ack was negotiated and
> multiqueue enabled. These Qemu version are now very old and no more
> maintained, so we can resonnably consider we no more support them.
> 
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
> 
> v2:
>  - Fix commit message
>  - Remove mention to the workaround in the doc
> 
>  doc/guides/prog_guide/vhost_lib.rst | 5 -----
>  lib/librte_vhost/vhost_user.c       | 9 ---------
>  2 files changed, 14 deletions(-)
> 
> diff --git a/doc/guides/prog_guide/vhost_lib.rst
> b/doc/guides/prog_guide/vhost_lib.rst
> index 07e40e3c5e..db921f922b 100644
> --- a/doc/guides/prog_guide/vhost_lib.rst
> +++ b/doc/guides/prog_guide/vhost_lib.rst
> @@ -104,11 +104,6 @@ The following is an overview of some key Vhost API
> functions:
>      from accessing memory the virtio device isn't allowed to, when the feature
>      is negotiated and an IOMMU device is declared.
> 
> -    However, this feature enables vhost-user's reply-ack protocol feature,
> -    which implementation is buggy in Qemu v2.7.0-v2.9.0 when doing multiqueue.
> -    Enabling this flag with these Qemu version results in Qemu being blocked
> -    when multiple queue pairs are declared.
> -
>    - ``RTE_VHOST_USER_POSTCOPY_SUPPORT``
> 
>      Postcopy live-migration support will be enabled when this flag is set.
> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c index
> 84bebad792..ea9cd107b9 100644
> --- a/lib/librte_vhost/vhost_user.c
> +++ b/lib/librte_vhost/vhost_user.c
> @@ -2012,15 +2012,6 @@ vhost_user_get_protocol_features(struct virtio_net
> **pdev,
>  	rte_vhost_driver_get_features(dev->ifname, &features);
>  	rte_vhost_driver_get_protocol_features(dev->ifname,
> &protocol_features);
> 
> -	/*
> -	 * REPLY_ACK protocol feature is only mandatory for now
> -	 * for IOMMU feature. If IOMMU is explicitly disabled by the
> -	 * application, disable also REPLY_ACK feature for older buggy
> -	 * Qemu versions (from v2.7.0 to v2.9.0).
> -	 */
> -	if (!(features & (1ULL << VIRTIO_F_IOMMU_PLATFORM)))
> -		protocol_features &= ~(1ULL <<
> VHOST_USER_PROTOCOL_F_REPLY_ACK);
> -
>  	msg->payload.u64 = protocol_features;
>  	msg->size = sizeof(msg->payload.u64);
>  	msg->fd_num = 0;
> --
> 2.26.2

Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>