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

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Message-ID: <aVz-6WozGIxGiTUR@J2N7QTR9R3>
Date: Tue, 6 Jan 2026 12:24:09 +0000
From: Mark Rutland <mark.rutland@....com>
To: Breno Leitao <leitao@...ian.org>
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.
> 
> Regardless, I'm in favour of disabling CONFIG_DEBUG_VIRTUAL widely, so:
> 
> Acked-by: Mark Rutland <mark.rutland@....com>

Whoops; s/CONFIG_DEBUG_VIRTUAL/PROFILE_ANNOTATED_BRANCHES/ in both
places in my reply.

Mark.