[dpdk-dev] [PATCH v5] kni: add IOVA va support for kni

[Burakov, Anatoly]

On 22-Apr-19 7:15 AM, kirankumark at marvell.com wrote:
> From: Kiran Kumar K <kirankumark at marvell.com>
> 
> 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 get the physical address from iova address using
> api iommu_iova_to_phys. Using this API, we will get the physical
> address from iova address and later use phys_to_virt API to
> convert the physical address to kernel virtual address.
> 
> With this approach we have compared the performance with IOVA=PA
> and there is no difference observed. Seems like kernel is the
> overhead.
> 
> This approach will not work with the kernel versions less than 4.4.0
> because of API compatibility issues.
> 
> Signed-off-by: Kiran Kumar K <kirankumark at marvell.com>
> ---

<snip>

> diff --git a/kernel/linux/kni/kni_net.c b/kernel/linux/kni/kni_net.c
> index be9e6b0b9..e77a28066 100644
> --- a/kernel/linux/kni/kni_net.c
> +++ b/kernel/linux/kni/kni_net.c
> @@ -35,6 +35,22 @@ static void kni_net_rx_normal(struct kni_dev *kni);
>   /* kni rx function pointer, with default to normal rx */
>   static kni_net_rx_t kni_net_rx_func = kni_net_rx_normal;
> 
> +/* iova to kernel virtual address */
> +static void *
> +iova2kva(struct kni_dev *kni, void *pa)
> +{
> +	return phys_to_virt(iommu_iova_to_phys(kni->domain,
> +				(uintptr_t)pa));
> +}
> +
> +static void *
> +iova2data_kva(struct kni_dev *kni, struct rte_kni_mbuf *m)
> +{
> +	return phys_to_virt((iommu_iova_to_phys(kni->domain,
> +					(uintptr_t)m->buf_physaddr) +
> +			     m->data_off));
> +}
> +

Apologies, i've accidentally responded to the previous version with this 
comment.

I don't see how this could possibly work, because for any 
IOVA-contiguous chunk of memory, mbufs are allowed to cross page 
boundaries. In this function, you're getting the start address of a 
buffer, but there are no guarantees that the end of the buffer is on the 
same physical page.

-- 
Thanks,
Anatoly