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

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 29-Sep-21 7:12 AM, Hu, Jiayu wrote:
> 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?

Unsupported as in the VFIO driver is not loaded. We don't really care if 
the *system* supports VFIO as much as whether it's *accessible to us*. 
I'm sure you would agree that scenario "VFIO is not supported" is 
exactly equivalent to "VFIO driver is not loaded", because from our 
perspective, in both cases the VFIO driver is not loaded :)

> 
> Thanks,
> Jiayu
> 


-- 
Thanks,
Anatoly