netdev - Re: [PATCH bpf-next 1/7] nfp: bpf: allow source ptr type be map ptr in memcpy optimization

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Date:   Tue, 26 Jun 2018 00:08:30 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Song Liu <liu.song.a23@...il.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        oss-drivers@...ronome.com, Networking <netdev@...r.kernel.org>,
        Jiong Wang <jiong.wang@...ronome.com>
Subject: Re: [PATCH bpf-next 1/7] nfp: bpf: allow source ptr type be map ptr
 in memcpy optimization

On Mon, Jun 25, 2018 at 10:50 PM, Song Liu <liu.song.a23@...il.com> wrote:
> On Sun, Jun 24, 2018 at 8:54 PM, Jakub Kicinski
> <jakub.kicinski@...ronome.com> wrote:
>> From: Jiong Wang <jiong.wang@...ronome.com>
>>
>> Map read has been supported on NFP, this patch enables optimization for
>> memcpy from map to packet.
>>
>> This patch also fixed one latent bug which will cause copying from
>> unexpected address once memcpy for map pointer enabled.
>>
>> Reported-by: Mary Pham <mary.pham@...ronome.com>
>> Reported-by: David Beckett <david.beckett@...ronome.com>
>> Signed-off-by: Jiong Wang <jiong.wang@...ronome.com>
>> Reviewed-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
>> ---
>>  drivers/net/ethernet/netronome/nfp/bpf/jit.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/netronome/nfp/bpf/jit.c b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
>> index 8a92088df0d7..33111739b210 100644
>> --- a/drivers/net/ethernet/netronome/nfp/bpf/jit.c
>> +++ b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
>> @@ -670,7 +670,7 @@ static int nfp_cpp_memcpy(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
>>         xfer_num = round_up(len, 4) / 4;
>>
>>         if (src_40bit_addr)
>> -               addr40_offset(nfp_prog, meta->insn.src_reg, off, &src_base,
>> +               addr40_offset(nfp_prog, meta->insn.src_reg * 2, off, &src_base,
>>                               &off);
>
> Did this break other cases before this patch?
>
> I am sorry if this is a dumb question. I don't think I fully
> understand addr40_offset().

Only map memory uses 40 bit addressing right now, so the if was pretty
much dead code before the patch.

The memcpy optimization was left out of the initial map support due to
insufficient test coverage, I should have probably left more of the 40
bit addressing code out back then.