> -----Original Message-----
> From: Ferruh Yigit <ferruh.yi...@intel.com>
> Sent: Wednesday, April 3, 2019 9:59 PM
> To: Kiran Kumar Kokkilagadda <kirankum...@marvell.com>
> Cc: dev@dpdk.org; Jerin Jacob <jerin.ja...@caviumnetworks.com>
> Subject: [EXT] Re: [dpdk-dev] [PATCH v2] kni: add IOVA va support for kni
>
> External Email
>
> ----------------------------------------------------------------------
> On 4/1/2019 10:51 AM, Kiran Kumar Kokkilagadda wrote:
> > From: Kiran Kumar K <kirankum...@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.
>
> Thanks Kiran for removing the limitation, I have a few questions, can you
> please
> help me understand.
>
> And when this patch is ready, the restriction in 'linux/eal/eal.c', in
> 'rte_eal_init'
> should be removed, perhaps with this patch. I assume you already doing it to
> be
> able to test this patch.
>
User can choose the mode by passing --iova-mode=<va/pa>. I will remove the
rte_kni module restriction.
> >
> > 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).
>
> Is it?
> As far as I know mempool can have multiple chunks and they can be both
> virtually and physically separated.
>
> And even for a single chunk, that will be virtually continuous, but will it be
> physically continuous?
>
You are right, it need not have to be physically contiguous. Will change the
description.
> >
> > 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 K <kirankum...@marvell.com>
>
> <...>
>
> > +int
> > +kni_pin_pages(void *address, size_t size, struct page_info *mem) {
> > + unsigned int gup_flags = FOLL_WRITE;
> > + long npgs;
> > + int err;
> > +
> > + /* Get at least one page */
> > + if (size < PAGE_SIZE)
> > + size = PAGE_SIZE;
> > +
> > + /* Compute number of user pages based on page size */
> > + mem->npgs = (size + PAGE_SIZE - 1) / PAGE_SIZE;
> > +
> > + /* Allocate memory for the pages */
> > + mem->pgs = kcalloc(mem->npgs, sizeof(*mem->pgs),
> > + GFP_KERNEL | __GFP_NOWARN);
> > + if (!mem->pgs) {
> > + pr_err("%s: -ENOMEM\n", __func__);
> > + return -ENOMEM;
> > + }
> > +
> > + down_write(¤t->mm->mmap_sem);
> > +
> > + /* Get the user pages from the user address*/ #if
> LINUX_VERSION_CODE
> > +>= KERNEL_VERSION(4,9,0)
> > + npgs = get_user_pages((u64)address, mem->npgs,
> > + gup_flags, &mem->pgs[0], NULL);
> > +#else
> > + npgs = get_user_pages(current, current->mm, (u64)address, mem-
> >npgs,
> > + gup_flags, 0, &mem->pgs[0], NULL); #endif
> > + up_write(¤t->mm->mmap_sem);
>
> This should work even memory is physically not continuous, right? Where
> exactly physically continuous requirement is coming from?
>
Yes, it is not necessary to be physically contiguous.
> <...>
>
> > +
> > +/* Get the kernel address from the user address using
> > + * page map table. Will be used only in IOVA=VA mode */ static
> > +inline void* get_kva(uint64_t usr_addr, struct kni_dev *kni) {
> > + uint32_t index;
> > + /* User page - start user page will give the index
> > + * with in the page map table
> > + */
> > + index = (usr_addr >> PAGE_SHIFT) - kni->va_info.start_page;
> > +
> > + /* Add the offset to the page address */
> > + return (kni->va_info.page_map[index].addr +
> > + (usr_addr & kni->va_info.page_mask));
> > +
> > +}
> > +
> > /* physical address to kernel virtual address */ static void *
> > pa2kva(void *pa) @@ -186,7 +205,10 @@ kni_fifo_trans_pa2va(struct
> > kni_dev *kni,
> > return;
> >
> > for (i = 0; i < num_rx; i++) {
> > - kva = pa2kva(kni->pa[i]);
> > + if (likely(kni->iova_mode == 1))
> > + kva = get_kva((u64)(kni->pa[i]), kni);
>
> kni->pa[] now has iova addresses, for 'get_kva()' to work shouldn't
> 'va_info.start_page' calculated from 'mempool_memhdr->iova' instead of
> 'mempool_memhdr->addr'
>
> If this is working I must be missing something but not able to find what it
> is.
>
> <...>
>
In IOVA=VA mode, both the values will be same right?
> > @@ -304,6 +304,27 @@ rte_kni_alloc(struct rte_mempool *pktmbuf_pool,
> > kni->group_id = conf->group_id;
> > kni->mbuf_size = conf->mbuf_size;
> >
> > + dev_info.iova_mode = (rte_eal_iova_mode() == RTE_IOVA_VA) ? 1 : 0;
> > + if (dev_info.iova_mode) {
> > + struct rte_mempool_memhdr *hdr;
> > + uint64_t pool_size = 0;
> > +
> > + /* In each pool header chunk, we will maintain the
> > + * base address of the pool. This chunk is physically and
> > + * virtually contiguous.
> > + * This approach will work, only if the allocated pool
> > + * memory is contiguous, else it won't work
> > + */
> > + hdr = STAILQ_FIRST(&pktmbuf_pool->mem_list);
> > + dev_info.mbuf_va = (void *)(hdr->addr);
> > +
> > + /* Traverse the list and get the total size of the pool */
> > + STAILQ_FOREACH(hdr, &pktmbuf_pool->mem_list, next) {
> > + pool_size += hdr->len;
> > + }
>
> This code is aware that there may be multiple chunks, but assumes they are all
> continuous, I don't know if this assumption is correct.
>
> Also I guess there is another assumption that there will be single
> pktmbuf_pool
> in the application which passed into kni?
> What if there are multiple pktmbuf_pool, like one for each PMD, will this
> work?
> Now some mbufs in kni Rx fifo will come from different pktmbuf_pool which we
> don't know their pages, so won't able to get their kernel virtual address.
All these chunks have to be virtually contiguous, otherwise this approach will
not work. Here one thing we can do is create the mapping for complete huge
page, and make sure all the mbuff_mempools will be with in this offset. As huge
page size will be big (x64 it is 1G, ARM 512MB), we may not exceed the size,
even with multiple pktmbuf_pools. If mbuf_pools were created outside this
huge_page, this approach will not work and we will fall back to PA mode.
