netdev - Re: [PATCH bpf-next v5 4/5] bpf: verifier: Support eliding map lookup nullness

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Message-ID: <aur6exve4ytjvrdpf6o3k74plqktc3ke4kmdqnrlrhiljtq72x@irruxegpbsce>
Date: Wed, 18 Dec 2024 17:09:30 -0700
From: Daniel Xu <dxu@...uu.xyz>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Eduard Zingerman <eddyz87@...il.com>, andrii@...nel.org, 
	ast@...nel.org, shuah@...nel.org, daniel@...earbox.net, john.fastabend@...il.com, 
	martin.lau@...ux.dev, song@...nel.org, yonghong.song@...ux.dev, kpsingh@...nel.org, 
	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, mykolal@...com, 
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 4/5] bpf: verifier: Support eliding map
 lookup nullness

On Mon, Dec 16, 2024 at 03:24:01PM -0800, Andrii Nakryiko wrote:
> On Fri, Dec 13, 2024 at 7:13 PM Eduard Zingerman <eddyz87@...il.com> wrote:
> >
> > On Fri, 2024-12-13 at 19:44 -0700, Daniel Xu wrote:
> >

[...]

> >
> > > > with Eduard's suggestion this also becomes interesting when you have
> > > > 000mmm mix (as one example), because that gives you a small range, and
> > > > all values might be valid keys for arrays
> > >
> > > Can you define what "small range" means? What range is there with 0's?
> > > Any pointers would be helpful.
> >
> > I think Andrii means that each 'm' adds 8 bits of range.
> > E.g. range for 0000_000m is 0-255, range for 0000_00mm is 0-65535, etc.
> 
> yes, exactly, thank you, Eduard!

Gave it some thought. Still seems like a good idea, but I'd prefer to
leave this extension for a separate patchset. Mostly b/c I'm running out
of space in my head to grok everything :P. Probably higher likelihood of
me getting the existing stuff correct if I don't add more scope.

Thanks,
Daniel