netdev - Re: [PATCH] bpf: optimize constant blinding

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Date:   Wed, 12 Jun 2019 08:28:22 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jiong Wang <jiong.wang@...ronome.com>
Cc:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: Re: [PATCH] bpf: optimize constant blinding

On Wed, Jun 12, 2019 at 8:25 AM Jiong Wang <jiong.wang@...ronome.com> wrote:
>
>
> Jiong Wang writes:
>
> > Alexei Starovoitov writes:
> >
> >> On Wed, Jun 12, 2019 at 4:32 AM Naveen N. Rao
> >> <naveen.n.rao@...ux.vnet.ibm.com> wrote:
> >>>
> >>> Currently, for constant blinding, we re-allocate the bpf program to
> >>> account for its new size and adjust all branches to accommodate the
> >>> same, for each BPF instruction that needs constant blinding. This is
> >>> inefficient and can lead to soft lockup with sufficiently large
> >>> programs, such as the new verifier scalability test (ld_dw: xor
> >>> semi-random 64 bit imms, test 5 -- with net.core.bpf_jit_harden=2)
> >>
> >> Slowdown you see is due to patch_insn right?
> >> In such case I prefer to fix the scaling issue of patch_insn instead.
> >> This specific fix for blinding only is not addressing the core of the problem.
> >> Jiong,
> >> how is the progress on fixing patch_insn?
>
> And what I have done is I have digested your conversion with Edward, and is
> slightly incline to the BB based approach as it also exposes the inserted
> insn to later pass in a natural way, then was trying to find a way that
> could create BB info in little extra code based on current verifier code,
> for example as a side effect of check_subprogs which is doing two insn
> traversal already. (I had some such code before in the historical
> wip/bpf-loop-detection branch, but feel it might be still too heavy for
> just improving insn patching)

BB - basic block?
I'm not sure that was necessary.
The idea was that patching is adding stuff to linked list instead
and single pass at the end to linearize it.