linux-kernel - Re: [RFC PATCH 0/5] pgo: Add PGO support for module profile data

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Message-ID: <202106140904.484E2337C@keescook>
Date:   Mon, 14 Jun 2021 09:05:40 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jarmo Tiitto <jarmo.tiitto@...il.com>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Bill Wendling <wcw@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org,
        morbo@...gle.com
Subject: Re: [RFC PATCH 0/5] pgo: Add PGO support for module profile data

[oops, I failed to CC correctly -- resending]

On Sat, Jun 12, 2021 at 06:24:21AM +0300, Jarmo Tiitto wrote:
> This patch series intends to extend the current Clang PGO code to
> support profile data from modules. Note that current PGO can and *does* 
> instrument all kernel code, including modules, but this profile data
> is inaccessible.
> 
> This patch series adds pgo/<module>.profraw files from what
> per loaded module profile data can be read.
> 
> The final profile can be generated by merging all these profile files:
> llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw ...
> and then building the optimized kernel.
> 
> This v2 patch series is still an bit of RFC so I'd like feedback how
> to do things better still.

This looks pretty good; thank you! I sent some notes, which are mostly
just clean-ups and patch hunk moves.

> The patches itself are based on Kees/for-next/clang/features tree
> where I have two of my bug fix patches already in. :-)
> 
> I have done some initial testing:
>  * Booted the instrumented kernel on qemu *and* bare hardware.
>  * Module un/loading via test_module in QEMU.
>  * Built optimized kernel using the new profile data.

If you haven't already, can you also test this with lock testing
enabled? i.e. these configs:

# Detect potential deadlocks.
CONFIG_PROVE_LOCKING=y
# Detect sleep-while-atomic.
CONFIG_DEBUG_ATOMIC_SLEEP=y

Thanks!

-Kees

> 
> Jarmo Tiitto (5):
>   pgo: Expose module sections for clang PGO instumentation.
>   pgo: Make serializing functions to take prf_object
>   pgo: Wire up the new more generic code for modules
>   pgo: Add module notifier machinery
>   pgo: Cleanup code in pgo/fs.c
> 
>  include/linux/module.h  |  15 +++
>  kernel/Makefile         |   6 +
>  kernel/module.c         |   7 ++
>  kernel/pgo/fs.c         | 241 ++++++++++++++++++++++++++++++++++------
>  kernel/pgo/instrument.c |  57 +++++++---
>  kernel/pgo/pgo.h        |  85 ++++++++++----
>  6 files changed, 342 insertions(+), 69 deletions(-)
> 
> 
> base-commit: 0039303120c0065f3952698597e0c9916b76ebd5
> -- 
> 2.32.0
> 

-- 
Kees Cook