netdev - Re: [PATCH bpf] nfp: bpf: fix latency bug when updating stack index register

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1417962c-e63d-6c46-bf07-9284f5332583@iogearbox.net>
Date:   Mon, 26 Aug 2019 18:25:10 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Song Liu <liu.song.a23@...il.com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        OSS Drivers <oss-drivers@...ronome.com>,
        Jiong Wang <jiong.wang@...ronome.com>
Subject: Re: [PATCH bpf] nfp: bpf: fix latency bug when updating stack index
 register

On 8/26/19 6:18 PM, Alexei Starovoitov wrote:
> On Mon, Aug 26, 2019 at 8:57 AM Jakub Kicinski
> <jakub.kicinski@...ronome.com> wrote:
>> On Sun, Aug 25, 2019 at 10:37 PM Song Liu <liu.song.a23@...il.com> wrote:
>>> On Fri, Aug 23, 2019 at 7:04 PM Jakub Kicinski wrote:
>>>> From: Jiong Wang <jiong.wang@...ronome.com>
>>>>
>>>> NFP is using Local Memory to model stack. LM_addr could be used as base of
>>>> a 16 32-bit word region of Local Memory. Then, if the stack offset is
>>>> beyond the current region, the local index needs to be updated. The update
>>>> needs at least three cycles to take effect, therefore the sequence normally
>>>> looks like:
>>>>
>>>>    local_csr_wr[ActLMAddr3, gprB_5]
>>>>    nop
>>>>    nop
>>>>    nop
>>>>
>>>> If the local index switch happens on a narrow loads, then the instruction
>>>> preparing value to zero high 32-bit of the destination register could be
>>>> counted as one cycle, the sequence then could be something like:
>>>>
>>>>    local_csr_wr[ActLMAddr3, gprB_5]
>>>>    nop
>>>>    nop
>>>>    immed[gprB_5, 0]
>>>>
>>>> However, we have zero extension optimization that zeroing high 32-bit could
>>>> be eliminated, therefore above IMMED insn won't be available for which case
>>>> the first sequence needs to be generated.
>>>>
>>>> Fixes: 0b4de1ff19bf ("nfp: bpf: eliminate zero extension code-gen")
>>>> Signed-off-by: Jiong Wang <jiong.wang@...ronome.com>
>>>> Reviewed-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
>>> I haven't looked into the code yet. But ^^^ should be
>>>
>>> Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
>>>
>>> right?
>>
>> I prefer Review on code I review, ack on code I ack, and sign-off on
>> code I co-author.
> 
> I believe if you're sending somebody else patch you have to add your SOB
> in addition to their 'Author:' and their SOB fields.

+1, for co-authoring there's a 'Co-authored-by:' tag which seems to be frequently
used these days.