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

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 4/1/2019 6:30 PM, Jerin Jacob Kollanukkaran wrote:
> 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.
> 

Hi Jerin,

I will check it, I remember the request, thanks for the patch.