Re: [dpdk-dev] vhost: initializing iotlb memory only when IOMMU feature is enabled.

[Ilya Maximets <i.maximets@samsung.com>]

On 17.08.2018 23:19, Nitin Katiyar wrote:
> DPDK 17.11 introduced the IOMMU feature which caused additional
> DPDK memory requirement per vhostuser device as part of
> iotlb_init(). Today this is done unconditionally (from DPDK
> 17.11 onwards) i.e. irrespective of IOMMU feature being
> enabled on the vhostuser device, iotlb is initialized. This
> breaks the backward compatibility for applications like OVS
> due to increase in the DPDK memory footprint and causes upgrade
> failures.
>> This patch is to do iotlb_init only if IOMMU feature is
> enabled on device.

I guess, "Fixes" line should be here?

> 
> Signed-off-by: Nitin Katiyar <nitin.katiyar@ericsson.com>
> ---
>  lib/librte_vhost/iotlb.c      | 7 +++++++
>  lib/librte_vhost/vhost_user.c | 6 ++++++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/lib/librte_vhost/iotlb.c b/lib/librte_vhost/iotlb.c
> index c6354fe..befa2d3 100644
> --- a/lib/librte_vhost/iotlb.c
> +++ b/lib/librte_vhost/iotlb.c
> @@ -317,6 +317,13 @@ struct vhost_iotlb_entry {
>  	struct vhost_virtqueue *vq = dev->virtqueue[vq_index];
>  	int socket = 0;
>  
> +	if (!(dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))) {

vhost_user_iotlb_init() is called on the virtqueue allocation
stage, most likely while processing VHOST_USER_SET_VRING_CALL.
QEMU usually sends VHOST_USER_SET_FEATURES after the
VHOST_USER_SET_VRING_CALL. This means that 'dev->features' are
not yet initialized here.

Have you tested that IOMMU feature works with this patch applied?

> +		RTE_LOG(INFO, VHOST_CONFIG,
> +			"IOMMU feature is not enabled for this dev(%s)\n",
> +			dev->ifname);
> +		return 0;
> +	}
> +
>  	if (vq->iotlb_pool) {
>  		/*
>  		 * The cache has already been initialized,
> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> index a2d4c9f..7553a03 100644
> --- a/lib/librte_vhost/vhost_user.c
> +++ b/lib/librte_vhost/vhost_user.c
> @@ -1366,6 +1366,12 @@
>  	uint16_t i;
>  	uint64_t vva, len;
>  
> +	if (!(dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))) {
> +		RTE_LOG(ERR, VHOST_CONFIG,
> +			"IOMMU feature is not enabled for this dev(%s)\n",
> +			dev->ifname);
> +		return -1;
> +	}
>  	switch (imsg->type) {
>  	case VHOST_IOTLB_UPDATE:
>  		len = imsg->size;
>