[dpdk-dev] [RFC] Add support for device dma mask
Alejandro Lucero
alejandro.lucero at netronome.com
Thu Jun 28 11:56:51 CEST 2018
On Thu, Jun 28, 2018 at 9:54 AM, Burakov, Anatoly <anatoly.burakov at intel.com
> wrote:
> On 27-Jun-18 5:52 PM, Alejandro Lucero wrote:
>
>>
>>
>> On Wed, Jun 27, 2018 at 2:24 PM, Burakov, Anatoly <
>> anatoly.burakov at intel.com <mailto:anatoly.burakov at intel.com>> wrote:
>>
>> On 27-Jun-18 11:13 AM, Alejandro Lucero wrote:
>>
>>
>>
>> On Wed, Jun 27, 2018 at 9:17 AM, Burakov, Anatoly
>> <anatoly.burakov at intel.com <mailto:anatoly.burakov at intel.com>
>> <mailto:anatoly.burakov at intel.com
>>
>> <mailto:anatoly.burakov at intel.com>>> wrote:
>>
>> On 26-Jun-18 6:37 PM, Alejandro Lucero wrote:
>>
>> This RFC tries to handle devices with addressing
>> limitations.
>> NFP devices
>> 4000/6000 can just handle addresses with 40 bits implying
>> problems for handling
>> physical address when machines have more than 1TB of
>> memory. But
>> because how
>> iovas are configured, which can be equivalent to physical
>> addresses or based on
>> virtual addresses, this can be a more likely problem.
>>
>> I tried to solve this some time ago:
>>
>> https://www.mail-archive.com/dev@dpdk.org/msg45214.html
>> <https://www.mail-archive.com/dev@dpdk.org/msg45214.html>
>> <https://www.mail-archive.com/
>> dev at dpdk.org/msg45214.html
>> <https://www.mail-archive.com/dev@dpdk.org/msg45214.html>>
>>
>> It was delayed because there was some changes in
>> progress with
>> EAL device
>> handling, and, being honest, I completely forgot about
>> this
>> until now, when
>> I have had to work on supporting NFP devices with DPDK
>> and
>> non-root users.
>>
>> I was working on a patch for being applied on main DPDK
>> branch
>> upstream, but
>> because changes to memory initialization during the
>> last months,
>> this can not
>> be backported to stable versions, at least the part
>> where the
>> hugepages iovas
>> are checked.
>>
>> I realize stable versions only allow bug fixing, and this
>> patchset could
>> arguably not be considered as so. But without this, it
>> could be,
>> although
>> unlikely, a DPDK used in a machine with more than 1TB,
>> and then
>> NFP using
>> the wrong DMA host addresses.
>>
>> Although virtual addresses used as iovas are more
>> dangerous, for
>> DPDK versions
>> before 18.05 this is not worse than with physical
>> addresses,
>> because iovas,
>> when physical addresses are not available, are based on a
>> starting address set
>> to 0x0.
>>
>>
>> You might want to look at the following patch:
>>
>> http://patches.dpdk.org/patch/37149/
>> <http://patches.dpdk.org/patch/37149/>
>> <http://patches.dpdk.org/patch/37149/
>> <http://patches.dpdk.org/patch/37149/>>
>>
>> Since this patch, IOVA as VA mode uses VA addresses, and
>> that has
>> been backported to earlier releases. I don't think there's
>> any case
>> where we used zero-based addresses any more.
>>
>>
>> But memsegs get the iova based on hugepages physaddr, and for VA
>> mode that is based on 0x0 as starting point.
>>
>> And as far as I know, memsegs iovas are what end up being used
>> for IOMMU mappings and what devices will use.
>>
>>
>> For when physaddrs are available, IOVA as PA mode assigns IOVA
>> addresses to PA, while IOVA as VA mode assigns IOVA addresses to VA
>> (both 18.05+ and pre-18.05 as per above patch, which was applied to
>> pre-18.05 stable releases).
>>
>> When physaddrs aren't available, IOVA as VA mode assigns IOVA
>> addresses to VA, both 18.05+ and pre-18.05, as per above patch.
>>
>>
>> This is right.
>>
>> If physaddrs aren't available and IOVA as PA mode is used, then i as
>> far as i can remember, even though technically memsegs get their
>> addresses set to 0x0 onwards, the actual addresses we get in
>> memzones etc. are RTE_BAD_IOVA.
>>
>>
>> This is not right. Not sure if this was the intention, but if PA mode and
>> physaddrs not available, this code inside vfio_type1_dma_map:
>>
>> if(rte_eal_iova_mode() == RTE_IOVA_VA)
>>
>> dma_map.iova = dma_map.vaddr;
>>
>> else
>>
>> dma_map.iova = ms[i].iova;
>>
>>
>> does the IOMMU mapping using the iovas and not the vaddr, with the iovas
>> starting at 0x0.
>>
>
> Yep, you're right, apologies. I confused this with no-huge option.
So, what do you think about the patchset? Could it be this applied to
stable versions?
I'll send a patch for current 18.05 code which will have the dma mask and
the hugepage check, along with changes for doing the mmaps below the dma
mask limit.
>
>
> --
> Thanks,
> Anatoly
>
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