Re: [RFC] Add support for device dma mask

On Wed, Jun 27, 2018 at 9:17 AM, Burakov, Anatoly <anatoly.burakov@intel.com

wrote:

On 26-Jun-18 6:37 PM, Alejandro Lucero wrote:

quoted

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

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/

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.

 Since 18.05, those iovas can, and usually are, higher than 1TB, as they

quoted

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