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

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 27-Sep-18 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>
> ---

<snip>

> +
> +	/* IOVA mode. 1 = VA, 0 = PA */
> +	uint8_t iova_mode;

Wouldn't it be easier to understand if the same values (e.g. iova_mode 
== RTE_IOVA_VA) were used here as they are in DPDK?

-- 
Thanks,
Anatoly