[dpdk-stable] [RFC] Add support for device dma mask

[Burakov, Anatoly]

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>> 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>
> 
>         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/>
> 
>     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.

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.

> 
> 
>       Since 18.05, those iovas can, and usually are, higher than 1TB, as
>     they
> 
>         are based on 64 bits address space addresses, and by default the
>         kernel uses a
>         starting point far higher than 1TB.
> 
>         This patchset applies to stable 17.11.3 but I will be happy to
>         submit patches, if
>         required, for other DPDK stable versions.
> 
> 
> 
> 
>     -- 
>     Thanks,
>     Anatoly
> 
> 


-- 
Thanks,
Anatoly