linux-kernel - Re: [PATCH v2] arm64: Disable branch profiling for all arm64 code

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Message-ID: <tj43kozcibuidfzoqzrvk6gsxylddfpyftkdiy7xb2zm7yncx5@z33xu7tavuts>
Date: Tue, 6 Jan 2026 06:05:37 -0800
From: Breno Leitao <leitao@...ian.org>
To: Mark Rutland <mark.rutland@....com>
Cc: Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Laura Abbott <labbott@...hat.com>, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, kernel-team@...a.com, 
	puranjay@...nel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] arm64: Disable branch profiling for all arm64 code

On Tue, Jan 06, 2026 at 12:21:47PM +0000, Mark Rutland wrote:
> On Tue, Jan 06, 2026 at 02:16:35AM -0800, Breno Leitao wrote:
> > The arm64 kernel doesn't boot with annotated branches
> > (PROFILE_ANNOTATED_BRANCHES) enabled and CONFIG_DEBUG_VIRTUAL together.
> > 
> > Bisecting it, I found that disabling branch profiling in arch/arm64/mm
> > solved the problem. Narrowing down a bit further, I found that
> > physaddr.c is the file that needs to have branch profiling disabled to
> > get the machine to boot.
> > 
> > I suspect that it might invoke some ftrace helper very early in the boot
> > process and ftrace is still not enabled(!?).
> > 
> > Rather than playing whack-a-mole with individual files, disable branch
> > profiling for the entire arch/arm64 tree, similar to what x86 already
> > does in arch/x86/Kbuild.
> > 
> > Cc: stable@...r.kernel.org
> > Fixes: ec6d06efb0bac ("arm64: Add support for CONFIG_DEBUG_VIRTUAL")
> > Signed-off-by: Breno Leitao <leitao@...ian.org>
> 
> I don't think ec6d06efb0bac is to blame here, and CONFIG_DEBUG_VIRTUAL
> is unsound in a number of places, so I'd prefer to remove that Fixes tag
> and backport this for all stable trees.

That is fair, thanks for the review.

Should I submit a new version without the fixes tag, or, do you guys do
it while merging the patch?

thanks
--breno