Re: [dpdk-dev] [PATH 0/5] use IOVAs check based on DMA mask

[Alejandro Lucero <alejandro.lucero@netronome.com>]

There is a problem with the patch due to a last-hour change regarding
MAX_DMA_MASK_BITS. It turns out initial X86_VA_WIDTH definition was to 47
bits, but it is not enough in some systems leading to IOVA VA not
available. Because MAX_DMA_MASK_BITS was just used for a sanity check about
the mask length, it is harmless to increment the value to 63 for 64-bits
systems, but I was really clumsy doing the change and it does not compile
now.

I've already set the patches as not applicable at patchwork and I will send
another version fixing that issue.



On Thu, Aug 30, 2018 at 5:21 PM, Alejandro Lucero <
alejandro.lucero@netronome.com> wrote:

> I sent a patchset about this to be applied on 17.11 stable. The memory
> code has had main changes since that version, so here it is the patchset
> adjusted to current master repo.
>
> This patchset adds, mainly, a check for ensuring IOVAs are within a
> restricted range due to addressing limitations with some devices. There
> are two known cases: NFP and IOMMU VT-d emulation.
>
> With this check IOVAs out of range are detected and PMDs can abort
> initialization. For the VT-d case, IOVA VA mode is allowed as long as
> IOVAs are within the supported range, avoiding to forbid IOVA VA by
> default.
>
> For the addressing limitations known cases, there are just 40(NFP) or
> 39(VT-d) bits for handling IOVAs. When using IOVA PA, those limitations
> imply 1TB(NFP) or 512M(VT-d) as upper limits, which is likely enough for
> most systems. With machines using more memory, the added check will
> ensure IOVAs within the range.
>
> With IOVA VA, and because the way the Linux kernel serves mmap calls
> in 64 bits systems, 39 or 40 bits are not enough. It is possible to
> give an address hint with a lower starting address than the default one
> used by the kernel, and then ensuring the mmap uses that hint or hint plus
> some offset. With 64 bits systems, the process virtual address space is
> large enoguh for doing the hugepages mmaping within the supported range
> when those addressing limitations exist. This patchset also adds a change
> for using such a hint making the use of IOVA VA a more than likely
> possibility when there are those addressing limitations.
>
> The check is not done by default but just when it is required. This
> patchset adds the check for NFP initialization and for setting the IOVA
> mode is an emulated VT-d is detected. Also, because the recent patchset
> adding dynamic memory allocation, the check is also invoked for ensuring
> the new memsegs are within the required range.
>
> This patchset could be applied to stable 18.05.
>
>