[dpdk-dev] [PATCH dpdk 5/5] RFC: vfio/ppc64/spapr: Use correct bus addresses for DMA map

[Alexey Kardashevskiy]

On 20/04/17 23:25, Alexey Kardashevskiy wrote:
> On 20/04/17 19:04, Jonas Pfefferle1 wrote:
>> Alexey Kardashevskiy <aik at ozlabs.ru> wrote on 20/04/2017 09:24:02:
>>
>>> From: Alexey Kardashevskiy <aik at ozlabs.ru>
>>> To: dev at dpdk.org
>>> Cc: Alexey Kardashevskiy <aik at ozlabs.ru>, JPF at zurich.ibm.com,
>>> Gowrishankar Muthukrishnan <gowrishankar.m at in.ibm.com>
>>> Date: 20/04/2017 09:24
>>> Subject: [PATCH dpdk 5/5] RFC: vfio/ppc64/spapr: Use correct bus
>>> addresses for DMA map
>>>
>>> VFIO_IOMMU_SPAPR_TCE_CREATE ioctl() returns the actual bus address for
>>> just created DMA window. It happens to start from zero because the default
>>> window is removed (leaving no windows) and new window starts from zero.
>>> However this is not guaranteed and the new window may start from another
>>> address, this adds an error check.
>>>
>>> Another issue is that IOVA passed to VFIO_IOMMU_MAP_DMA should be a PCI
>>> bus address while in this case a physical address of a user page is used.
>>> This changes IOVA to start from zero in a hope that the rest of DPDK
>>> expects this.
>>
>> This is not the case. DPDK expects a 1:1 mapping PA==IOVA. It will use the
>> phys_addr of the memory segment it got from /proc/self/pagemap cf.
>> librte_eal/linuxapp/eal/eal_memory.c. We could try setting it here to the
>> actual iova which basically makes the whole virtual to phyiscal mapping
>> with pagemap unnecessary which I believe should be the case for VFIO
>> anyway. Pagemap should only be needed when using pci_uio.
> 
> 
> Ah, ok, makes sense now. But it sure needs a big fat comment there as it is
> not obvious why host RAM address is used there as DMA window start is not
> guaranteed.

Well, either way there is some bug - ms[i].phys_addr and ms[i].addr_64 both
have exact same value, in my setup it is 3fffb33c0000 which is a userspace
address - at least ms[i].phys_addr must be physical address.


> 
> 
>>
>>>
>>> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
>>> ---
>>>  lib/librte_eal/linuxapp/eal/eal_vfio.c | 12 ++++++++++--
>>>  1 file changed, 10 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/lib/librte_eal/linuxapp/eal/eal_vfio.c b/lib/
>>> librte_eal/linuxapp/eal/eal_vfio.c
>>> index 46f951f4d..8b8e75c4f 100644
>>> --- a/lib/librte_eal/linuxapp/eal/eal_vfio.c
>>> +++ b/lib/librte_eal/linuxapp/eal/eal_vfio.c
>>> @@ -658,7 +658,7 @@ vfio_spapr_dma_map(int vfio_container_fd)
>>>  {
>>>     const struct rte_memseg *ms = rte_eal_get_physmem_layout();
>>>     int i, ret;
>>> -
>>> +   phys_addr_t io_offset;
>>>     struct vfio_iommu_spapr_register_memory reg = {
>>>        .argsz = sizeof(reg),
>>>        .flags = 0
>>> @@ -702,6 +702,13 @@ vfio_spapr_dma_map(int vfio_container_fd)
>>>        return -1;
>>>     }
>>>  
>>> +   io_offset = create.start_addr;
>>> +   if (io_offset) {
>>> +      RTE_LOG(ERR, EAL, "  DMA offsets other than zero is not supported, "
>>> +            "new window is created at %lx\n", io_offset);
>>> +      return -1;
>>> +   }
>>> +
>>>     /* map all DPDK segments for DMA. use 1:1 PA to IOVA mapping */
>>>     for (i = 0; i < RTE_MAX_MEMSEG; i++) {
>>>        struct vfio_iommu_type1_dma_map dma_map;
>>> @@ -723,7 +730,7 @@ vfio_spapr_dma_map(int vfio_container_fd)
>>>        dma_map.argsz = sizeof(struct vfio_iommu_type1_dma_map);
>>>        dma_map.vaddr = ms[i].addr_64;
>>>        dma_map.size = ms[i].len;
>>> -      dma_map.iova = ms[i].phys_addr;
>>> +      dma_map.iova = io_offset;
>>>        dma_map.flags = VFIO_DMA_MAP_FLAG_READ |
>>>               VFIO_DMA_MAP_FLAG_WRITE;
>>>  
>>> @@ -735,6 +742,7 @@ vfio_spapr_dma_map(int vfio_container_fd)
>>>           return -1;
>>>        }
>>>  
>>> +      io_offset += dma_map.size;
>>>     }
>>>  
>>>     return 0;
>>> --
>>> 2.11.0
>>>
>>
> 
> 


-- 
Alexey