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

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Message-Id: <20260106-annotated-v2-1-fb7600ebd47f@debian.org>
Date: Tue, 06 Jan 2026 02:16:35 -0800
From: Breno Leitao <leitao@...ian.org>
To: Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, 
 Laura Abbott <labbott@...hat.com>
Cc: 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, 
 Breno Leitao <leitao@...ian.org>
Subject: [PATCH v2] arm64: Disable branch profiling for all arm64 code

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>
---
Changes in v2:
- Expand the scope to arch/arm64 instead of just physaddr.c
- Link to v1: https://lore.kernel.org/all/20251231-annotated-v1-1-9db1c0d03062@debian.org/
---
 arch/arm64/Kbuild | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/Kbuild b/arch/arm64/Kbuild
index 5bfbf7d79c99..d876bc0e5421 100644
--- a/arch/arm64/Kbuild
+++ b/arch/arm64/Kbuild
@@ -1,4 +1,8 @@
 # SPDX-License-Identifier: GPL-2.0-only
+
+# Branch profiling isn't noinstr-safe
+subdir-ccflags-$(CONFIG_TRACE_BRANCH_PROFILING) += -DDISABLE_BRANCH_PROFILING
+
 obj-y			+= kernel/ mm/ net/
 obj-$(CONFIG_KVM)	+= kvm/
 obj-$(CONFIG_XEN)	+= xen/

---
base-commit: c8ebd433459bcbf068682b09544e830acd7ed222
change-id: 20251231-annotated-75de3f33cd7b

Best regards,
--  
Breno Leitao <leitao@...ian.org>