netdev - Re: [RFC PATCH 02/24] xsk: add user memory registration sockopt

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Date:   Wed, 7 Feb 2018 11:00:17 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        michael.lundkvist@...csson.com,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Singhai, Anjali" <anjali.singhai@...el.com>,
        "Shaw, Jeffrey B" <jeffrey.b.shaw@...el.com>,
        "Yigit, Ferruh" <ferruh.yigit@...el.com>,
        "Zhang, Qi Z" <qi.z.zhang@...el.com>
Subject: Re: [RFC PATCH 02/24] xsk: add user memory registration sockopt

On Wed, Jan 31, 2018 at 8:53 AM, Björn Töpel <bjorn.topel@...il.com> wrote:
> From: Björn Töpel <bjorn.topel@...el.com>
>
> The XDP_MEM_REG socket option allows a process to register a window of
> user space memory to the kernel. This memory will later be used as
> frame data buffer.
>
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
> ---

> +static struct xsk_umem *xsk_mem_reg(u64 addr, u64 size, u32 frame_size,
> +                                   u32 data_headroom)
> +{
> +       unsigned long lock_limit, locked, npages;
> +       int ret = 0;
> +       struct xsk_umem *umem;
> +
> +       if (!can_do_mlock())
> +               return ERR_PTR(-EPERM);
> +
> +       umem = xsk_umem_create(addr, size, frame_size, data_headroom);
> +       if (IS_ERR(umem))
> +               return umem;
> +
> +       npages = PAGE_ALIGN(umem->nframes * umem->frame_size) >> PAGE_SHIFT;
> +
> +       down_write(&current->mm->mmap_sem);
> +
> +       locked = npages + current->mm->pinned_vm;
> +       lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> +
> +       if (locked > lock_limit && !capable(CAP_IPC_LOCK)) {
> +               ret = -ENOMEM;
> +               goto out;
> +       }
> +
> +       if (npages == 0 || npages > UINT_MAX) {
> +               ret = -EINVAL;
> +               goto out;
> +       }
> +       umem->npgs = npages;
> +
> +       ret = xsk_umem_pin_pages(umem);
> +
> +out:
> +       if (ret < 0) {
> +               put_pid(umem->pid);
> +               kfree(umem);
> +       } else {
> +               current->mm->pinned_vm = locked;
> +       }
> +
> +       up_write(&current->mm->mmap_sem);

This limits per process. You may want to limit per user. See also
mm_account_pinned_pages.