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From:   Florent Revest <revest@chromium.org>
Date:   Thu, 3 Aug 2023 18:32:40 +0200
Message-ID: <CABRcYmLAjezx+awDicxYQkoim6JS1CQ-G_9+tJADudxNe3sutg@mail.gmail.com>
Subject: Re: [PATCH bpf-next v4 0/3] bpf, arm64: use BPF prog pack allocator
 in BPF JIT
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Puranjay Mohan <puranjay12@gmail.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        bpf <bpf@vger.kernel.org>, KP Singh <kpsingh@kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Aug 3, 2023 at 6:16=E2=80=AFPM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Thu, Aug 3, 2023 at 4:13=E2=80=AFAM Mark Rutland <mark.rutland@arm.com=
> wrote:
> >
> > Hi Alexei,
> >
> > On Wed, Aug 02, 2023 at 02:02:39PM -0700, Alexei Starovoitov wrote:
> > > Mark, Catalin, Florent, KP,

Maybe you've missed my Acked-by for the series Alexei ?
https://lore.kernel.org/all/CABRcYmLAzhG=3Do2wcBNBtFP34Aj3+eYsEMtMREDT7SqNz=
Bc9-qw@mail.gmail.com/

> > > This patch set was submitted on June 26 !
> >
> > I appreciate this was sent a while ago, but I have been stuck on some u=
rgent
> > bug-fixing for the last few weeks, and my review bandwidth is therfore =
very
> > limited.
> >
> > Given Puranjay had previously told me he was doing this as a side proje=
ct for
> > fun, and given no-one had told me this was urgent, I assumed that this =
wasn't a
> > major blocker and could wait.
> >
> > I should have sent a holding reply to that effect; sorry.
> >
> > The series addresses my original concern. However, in looking at it I t=
hink
> > there may me a wider potential isssue w.r.t. the way instruction memory=
 gets
> > reused, because as writtten today the architecture doesn't seem to have=
 a
> > guarantee on when instruction fetches are completed and therefore when =
it's
> > safe to modify instruction memory. Usually we're saved by TLB maintenan=
ce,
> > which this series avoids by design.

But I must say that this sits firmly outside of my knowledge of the
arm architectural details and I would totally miss this sort of nuance
so this is best handled by arm64 maintainers :)

> > I unfortunately haven't had the time to dig into that, poke our archite=
cts,
> > etc.
> >
> > So how urgent is this?
>
> The performance wins are substantial.
> We'd like to realize them sooner than later.

I've worked with Mark before, I know for a fact that he is dragged in
all directions. Until we figure out a way to clone him we should try
to not burn him out too often... :)