Re: [dpdk-dev] [PATCH v3 1/1] vfio: modify spapr iommu support to use static window sizing

[David Christensen <drc@linux.vnet.ibm.com>]

\>>>> -vfio_spapr_unmap_walk(const struct rte_memseg_list *msl,
>>>> -        const struct rte_memseg *ms, void *arg)
>>>> +vfio_spapr_size_walk(const struct rte_memseg_list *msl, void *arg)
>>>>   {
>>>> -    int *vfio_container_fd = arg;
>>>> +    struct spapr_size_walk_param *param = arg;
>>>> +    uint64_t max = (uint64_t) msl->base_va + (uint64_t) msl->len;
>>>> -    /* skip external memory that isn't a heap */
>>>> -    if (msl->external && !msl->heap)
>>>> -        return 0;
>>>> +    if (msl->external) {
>>>> +        param->external++;
>>>> +        if (!msl->heap)
>>>> +            return 0;
>>>> +    }
>>>
>>> It would be nice to have some comments in the code explaining what 
>>> we're skipping and why.
>>
>> Reviewing this again, my inclination is to skip ALL external memory, 
>> which by definition would seem to be outside of IOMMU control, so the 
>> code would read:
>>
>>     if (msl->external) {
>>         param->external++;
>>         return 0;
>>     }
> 
> The external memory can still be mapped for DMA with rte_dev_dma_map() 
> API. The heap memory is meant to be mapped automatically by DPDK, while 
> the non-heap memory (created with rte_extmem_register() API) is meant to 
> be managed by the user and will be mapped using the user_mem_map 
> functions in this file.

So for my purpose of identifying the memory range qualified for IOMMU 
protection, are you saying that external memory in the heap should be 
included in the DMA window calculation?  Like this:

         if (msl->external && !msl->heap) {
                 /* ignore user managed external memory */
                 param->is_user_managed = true;
                 return 0;
         }

Dave