Re: [dpdk-dev] [PATCH v6 2/2] vhost: enable IOMMU for async vhost

["Hu, Jiayu" <jiayu.hu@intel.com>]

Hi Xuan,

> -----Original Message-----
> From: Ding, Xuan <xuan.ding@intel.com>
> Sent: Wednesday, September 29, 2021 10:41 AM
> To: dev@dpdk.org; Burakov, Anatoly <anatoly.burakov@intel.com>;
> maxime.coquelin@redhat.com; Xia, Chenbo <chenbo.xia@intel.com>
> Cc: Hu, Jiayu <jiayu.hu@intel.com>; Jiang, Cheng1 <cheng1.jiang@intel.com>;
> Richardson, Bruce <bruce.richardson@intel.com>; Pai G, Sunil
> <sunil.pai.g@intel.com>; Wang, Yinan <yinan.wang@intel.com>; Yang,
> YvonneX <yvonnex.yang@intel.com>; Ding, Xuan <xuan.ding@intel.com>
> Subject: [PATCH v6 2/2] vhost: enable IOMMU for async vhost
> 
> The use of IOMMU has many advantages, such as isolation and address
> translation. This patch extends the capbility of DMA engine to use IOMMU if
> the DMA engine is bound to vfio.
> 
> When set memory table, the guest memory will be mapped into the default
> container of DPDK.
> 
> Signed-off-by: Xuan Ding <xuan.ding@intel.com>
> ---
> +async_dma_map(struct rte_vhost_mem_region *region, bool
> +*dma_map_success, bool do_map) {
> +	uint64_t host_iova;
> +	int ret = 0;
> +
> +	host_iova = rte_mem_virt2iova((void *)(uintptr_t)region-
> >host_user_addr);
> +	if (do_map) {
> +		/* Add mapped region into the default container of DPDK. */
> +		ret =
> rte_vfio_container_dma_map(RTE_VFIO_DEFAULT_CONTAINER_FD,
> +						 region->host_user_addr,
> +						 host_iova,
> +						 region->size);
> +		*dma_map_success = ret == 0;
> +
> +		if (ret) {
> +			/*
> +			 * DMA device may bind with kernel driver, in this
> case,
> +			 * we don't need to program IOMMU manually.
> However, if no
> +			 * device is bound with vfio/uio in DPDK, and vfio
> kernel
> +			 * module is loaded, the API will still be called and
> return
> +			 * with ENODEV/ENOSUP.
> +			 *
> +			 * DPDK vfio only returns ENODEV/ENOSUP in very
> similar
> +			 * situations(vfio either unsupported, or supported
> +			 * but no devices found). Either way, no mappings
> could be
> +			 * performed. We treat it as normal case in async
> path.
> +			 */


What do you mean by saying "vfio either unsupported"? Does it mean platform
doesn't support iommu?

Thanks,
Jiayu