netdev - Re: [PATCH bpf-next v5 03/11] xsk: add support to allow unaligned chunk placement

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Date:   Fri, 23 Aug 2019 14:35:40 +0100
From:   "Laatz, Kevin" <kevin.laatz@...el.com>
To:     Jonathan Lemon <jonathan.lemon@...il.com>
Cc:     netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        bjorn.topel@...el.com, magnus.karlsson@...el.com,
        jakub.kicinski@...ronome.com, saeedm@...lanox.com,
        maximmi@...lanox.com, stephen@...workplumber.org,
        bruce.richardson@...el.com, ciara.loftus@...el.com,
        bpf@...r.kernel.org, intel-wired-lan@...ts.osuosl.org
Subject: Re: [PATCH bpf-next v5 03/11] xsk: add support to allow unaligned
 chunk placement

On 22/08/2019 19:43, Jonathan Lemon wrote:
> On 21 Aug 2019, at 18:44, Kevin Laatz wrote:
>> Currently, addresses are chunk size aligned. This means, we are very
>> restricted in terms of where we can place chunk within the umem. For
>> example, if we have a chunk size of 2k, then our chunks can only be 
>> placed
>> at 0,2k,4k,6k,8k... and so on (ie. every 2k starting from 0).
>>
>> This patch introduces the ability to use unaligned chunks. With these
>> changes, we are no longer bound to having to place chunks at a 2k (or
>> whatever your chunk size is) interval. Since we are no longer dealing 
>> with
>> aligned chunks, they can now cross page boundaries. Checks for page
>> contiguity have been added in order to keep track of which pages are
>> followed by a physically contiguous page.
>>
>> Signed-off-by: Kevin Laatz <kevin.laatz@...el.com>
>> Signed-off-by: Ciara Loftus <ciara.loftus@...el.com>
>> Signed-off-by: Bruce Richardson <bruce.richardson@...el.com>
>>
>> ---
>> v2:
>>   - Add checks for the flags coming from userspace
>>   - Fix how we get chunk_size in xsk_diag.c
>>   - Add defines for masking the new descriptor format
>>   - Modified the rx functions to use new descriptor format
>>   - Modified the tx functions to use new descriptor format
>>
>> v3:
>>   - Add helper function to do address/offset masking/addition
>>
>> v4:
>>   - fixed page_start calculation in __xsk_rcv_memcpy().
>>   - move offset handling to the xdp_umem_get_* functions
>>   - modified the len field in xdp_umem_reg struct. We now use 16 bits 
>> from
>>     this for the flags field.
>>   - removed next_pg_contig field from xdp_umem_page struct. Using low 12
>>     bits of addr to store flags instead.
>>   - other minor changes based on review comments
>>
>> v5:
>>   - Added accessors for getting addr and offset
>>   - Added helper function to add offset to addr
>>   - Fixed offset handling in xsk_rcv
>>   - Removed bitfields from xdp_umem_reg
>>   - Added struct size checking for xdp_umem_reg in xsk_setsockopt to 
>> handle
>>     different versions of the struct.
>>   - fix conflicts after 'bpf-af-xdp-wakeup' was merged.
>> ---
>>  include/net/xdp_sock.h      | 75 +++++++++++++++++++++++++++--
>>  include/uapi/linux/if_xdp.h |  9 ++++
>>  net/xdp/xdp_umem.c          | 19 ++++++--
>>  net/xdp/xsk.c               | 96 +++++++++++++++++++++++++++++--------
>>  net/xdp/xsk_diag.c          |  2 +-
>>  net/xdp/xsk_queue.h         | 68 ++++++++++++++++++++++----
>>  6 files changed, 232 insertions(+), 37 deletions(-)
>>
>>
[...]

>> @@ -196,17 +221,17 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct 
>> xdp_buff *xdp)
>>          goto out_unlock;
>>      }
>>
>> -    if (!xskq_peek_addr(xs->umem->fq, &addr) ||
>> +    if (!xskq_peek_addr(xs->umem->fq, &addr, xs->umem) ||
>>          len > xs->umem->chunk_size_nohr - XDP_PACKET_HEADROOM) {
>>          err = -ENOSPC;
>>          goto out_drop;
>>      }
>>
>> -    addr += xs->umem->headroom;
>> -
>> -    buffer = xdp_umem_get_data(xs->umem, addr);
>> +    buffer = xdp_umem_get_data(xs->umem, addr + offset);
>>      memcpy(buffer, xdp->data_meta, len + metalen);
>> -    addr += metalen;
>> +    offset += metalen;
>> +
>> +    addr = xsk_umem_adjust_offset(xs->umem, addr, offset);
>>      err = xskq_produce_batch_desc(xs->rx, addr, len);
>>      if (err)
>>          goto out_drop;
>
> Can't just add address and offset any longer.  This should read:
>
>     addr = xsk_umem_adjust_offset(xs->umem, addr, offset);
>     buffer = xdp_umem_get_data(xs->umem, addr);
>
>     addr = xsk_umem_adjust_offset(xs->umem, addr, metalen);
>
>
> so that offset and then metalen are added.  (or preserve the
> address across the calls like memcpy_addr earlier).


Will fix this, thanks!

-Kevin