linux-kernel - Re: [PATCH 0/7] RFC: coverage deduplication for KCOV

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Message-ID: <CAG_fn=WyvDopbDN3YrrUzS-aUgbVKTDRv6D5vArnQbSkp_xB6Q@mail.gmail.com>
Date: Thu, 17 Apr 2025 14:43:56 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Joey Jiao <quic_jiangenj@...cinc.com>
Cc: linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com, 
	Aleksandr Nogikh <nogikh@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Dmitry Vyukov <dvyukov@...gle.com>, 
	Ingo Molnar <mingo@...hat.com>, Josh Poimboeuf <jpoimboe@...nel.org>, Marco Elver <elver@...gle.com>, 
	Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 0/7] RFC: coverage deduplication for KCOV

> > Below are the average stats from the runs.
> Is there test without trace collection? Is bitmap only enough?

If we bump the bitmap size to ~16K, it should be enough to keep all
the fuzzing results from a single run.
We haven't experimented with it much though, because syzkaller
currently processes coverage as an array of PCs, not a bitmap.
Changing this would require a major rework of syzkaller, given that
the positions in the bitmap may differ between different machines, so
we'll need to maintain a reverse mapping between bits and PCs in every
executor.

Such a mapping could be implemented on the kernel side on top of the
proposed patches, once someone proves a need for that.