Re: [dpdk-dev] [PATCH] kni: add IOVA va support for kni

[Jerin Jacob Kollanukkaran <jerinj@marvell.com>]

On Tue, 2018-10-02 at 18:05 +0100, Ferruh Yigit wrote:
> On 9/27/2018 11:49 AM, Kiran Kumar wrote:
> > With current KNI implementation kernel module will work only in
> > IOVA=PA mode. This patch will add support for kernel module to work
> > with IOVA=VA mode.
> > 
> > The idea is to maintain a mapping in KNI module between user pages
> > and
> > kernel pages and in fast path perform a lookup in this table and
> > get
> > the kernel virtual address for corresponding user virtual address.
> > 
> > In IOVA=VA mode, the memory allocated to the pool is physically
> > and virtually contiguous. We will take advantage of this and create
> > a
> > mapping in the kernel.In kernel we need mapping for queues
> > (tx_q, rx_q,... slow path) and mbuf memory (fast path).
> > 
> > At the KNI init time, in slow path we will create a mapping for the
> > queues and mbuf using get_user_pages similar to af_xdp. Using pool
> > memory base address, we will create a page map table for the mbuf,
> > which we will use in the fast path for kernel page translation.
> > 
> > At KNI init time, we will pass the base address of the pool and
> > size of
> > the pool to kernel. In kernel, using get_user_pages API, we will
> > get
> > the pages with size PAGE_SIZE and store the mapping and start
> > address
> > of user space in a table.
> > 
> > In fast path for any user address perform PAGE_SHIFT
> > (user_addr >> PAGE_SHIFT) and subtract the start address from this
> > value,
> > we will get the index of the kernel page with in the page map
> > table.
> > Adding offset to this kernel page address, we will get the kernel
> > address
> > for this user virtual address.
> > 
> > For example user pool base address is X, and size is S that we
> > passed to
> > kernel. In kernel we will create a mapping for this using
> > get_user_pages.
> > Our page map table will look like [Y, Y+PAGE_SIZE, Y+(PAGE_SIZE*2)
> > ....]
> > and user start page will be U (we will get it from X >>
> > PAGE_SHIFT).
> > 
> > For any user address Z we will get the index of the page map table
> > using
> > ((Z >> PAGE_SHIFT) - U). Adding offset (Z & (PAGE_SIZE - 1)) to
> > this
> > address will give kernel virtual address.
> > 
> > Signed-off-by: Kiran Kumar <kkokkilagadda@caviumnetworks.com>
> 
> Hi Kiran,
> 
> Thanks for the patch but it was later for this release, missed
> proposal deadline
> etc.. Taking the time remaining for integration deadline, this patch
> will be
> considered for next release.

Hi Ferruh,

This patch submitted in Oct last year. Could you please review this?
This feature was added based on community request to support IOVA for
KNI as Initial IOVA support doesn;t have KNI support.



> 
> Thanks,
> ferruh
>