[PATCH 6.6.y] ACPI: processor_idle: Mark LPI enter functions as __cpuidle

[Artem Dinaburg <artem@trailofbits.com>]

From: Li RongQing <lirongqing@baidu.com>

[ Upstream commit 956ca5d72c76504824c8eb601879da9476973e15 ]

When function tracing or Kprobes is enabled, entering an ACPI Low
Power Idle (LPI) state triggers the following RCU splat:

  RCU not on for: acpi_idle_lpi_enter+0x4/0xd8
  WARNING: CPU: 8 PID: 0 at include/linux/trace_recursion.h:162 function_trace_call+0x1e8/0x228

The acpi_idle_lpi_enter() function is invoked within the cpuidle
path after RCU has already been disabled for the current local CPU.
Consequently, ftrace's function_trace_call() expects RCU to be
actively watching before recording trace data, emitting a warning
if it is not.

Fix this by annotating acpi_idle_lpi_enter(), the generic __weak
stub, and the RISC-V implementation of acpi_processor_ffh_lpi_enter()
with __cpuidle. This moves these functions into the '.cpuidle.text'
section, implicitly disabling ftrace instrumentation (notrace) along
this sensitive path and preventing trace-induced RCU warnings during
idle entry.

Fixes: a36a7fecfe60 ("ACPI / processor_idle: Add support for Low Power Idle(LPI) states")
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Acked-by: lihuisong@huawei.com
Link: https://patch.msgid.link/20260616072617.2272-1-lirongqing@baidu.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Assisted-by: LLM
[ Backport to 6.6.y: Omit the RISC-V hunk because this target has no
  RISC-V ACPI LPI implementation. ]
Signed-off-by: Artem Dinaburg <artem@trailofbits.com>
---
Hi,

Please consider this backport of the fix for CVE-2026-80611 to 6.6.y.

The code changes are identical to upstream, except the absent RISC-V LPI
hunk is omitted. See the bracketed backport note above.

The complete fix is already present in 6.12.y, 6.18.y and 7.2.y.

Build-tested only as part of a cumulative 6.6.y series: the x86_64 ACPI
processor-idle object (allmodconfig, CONFIG_WERROR=y); no runtime testing.

Thanks,
Artem Dinaburg

 drivers/acpi/processor_idle.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index d755c266e3586750968ad7c4e01c5538ceb631e3..5db34356328c7e4e62b30fb53fca375e9e7d972f 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -1175,7 +1175,7 @@ static int acpi_processor_get_lpi_info(struct acpi_processor *pr)
 	return 0;
 }
 
-int __weak acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi)
+int __weak __cpuidle acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi)
 {
 	return -ENODEV;
 }
@@ -1188,7 +1188,7 @@ int __weak acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi)
  *
  * Return: 0 for success or negative value for error
  */
-static int acpi_idle_lpi_enter(struct cpuidle_device *dev,
+static int __cpuidle acpi_idle_lpi_enter(struct cpuidle_device *dev,
 			       struct cpuidle_driver *drv, int index)
 {
 	struct acpi_processor *pr;