Public bug reported:
What I expected to happen:
CPU scales up to its rated frequency (up to 4.8 GHz) under load.
What actually happened:
All cores are pinned at the hardware minimum under full load — P-cores 400 MHz,
E-cores 200 MHz — while the package is cold (~45 C). Governor and EPP set to
"performance", scaling_max_freq = 4.8 GHz, no_turbo = 0, so the OS is
requesting full speed. thermal_throttle/package_throttle_count does NOT
increment during the clamp, so it is not thermal throttling. RAM/swap/load are
all fine.
Root cause — BD PROCHOT asserted with no thermal reason:
$ sudo rdmsr -a 0x1FC
e4005b # MSR_POWER_CTL bit0 = 1 -> BD PROCHOT enabled
$ sudo rdmsr -a 0x1B1
8837000c # IA32_PACKAGE_THERM_STATUS, ...0c -> bit2 = 1 PROCHOT actively
asserted
# digital readout shows the CPU is cold
Key behaviour:
- A normal reboot does NOT clear it; PROCHOT stays asserted across warm
reboots (the EC appears to retain the state).
- A full shutdown + EC reset (power off, unplug charger, hold power button ~40
s, replug, power on) DOES clear it; the CPU then runs at full speed (3.8 GHz
P-cores / 3.7 GHz E-cores under load).
- The usual userspace workaround (sudo wrmsr -a 0x1FC 0xe4005a, clearing BD
PROCHOT enable bit) is blocked by kernel lockdown because Secure Boot is
enabled:
Lockdown: wrmsr: raw MSR access is restricted; see man kernel_lockdown.7
- NOT reproducible on Windows on the same machine/BIOS, which points to a
Linux-specific driver/firmware interaction.
Steps to reproduce:
1. Boot Ubuntu on an ASUS Zenbook S14 UX5406SA (Core Ultra 7 258V), Secure
Boot enabled.
2. Suspend (close lid) and resume — or simply observe after a warm reboot.
3. Run a CPU load and check: cat
/sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq -> pinned at
400000/200000.
4. sudo rdmsr -a 0x1B1 -> value ends in 0c (bit2 = PROCHOT asserted) while the
CPU is cold.
System:
- ASUS Zenbook S14 UX5406SA
- Intel Core Ultra 7 258V (Lunar Lake), family 6 model 189 stepping 1
- BIOS UX5406SA.308 (2025-06-05, latest available)
- Ubuntu 26.04 LTS, kernel 7.0.0-22-generic
- intel_pstate (HWP active), Secure Boot ON (lockdown=integrity)
Question: should an ASUS platform driver (asus-nb-wmi / asus_armoury) or
a Lunar Lake power/thermal driver be de-asserting this PROCHOT source on
resume/boot? Is there a fix that does not require disabling Secure Boot?
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: linux-image-7.0.0-22-generic 7.0.0-22.22
ProcVersionSignature: Ubuntu 7.0.0-22.22-generic 7.0.0
Uname: Linux 7.0.0-22-generic x86_64
ApportVersion: 2.34.0-0ubuntu2
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: ricardo-reis 4575 F.... pipewire
ricardo-reis 4600 F.... wireplumber
/dev/snd/controlC1: ricardo-reis 4600 F.... wireplumber
/dev/snd/seq: ricardo-reis 4575 F.... pipewire
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Sun Jun 14 13:52:13 2026
InstallationDate: Installed on 2026-04-24 (51 days ago)
InstallationMedia: Ubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423.1)
MachineType: ASUSTeK COMPUTER INC. ASUS Zenbook S 14 UX5406SA_UX5406SA
ProcEnviron:
LANG=pt_BR.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
XDG_RUNTIME_DIR=<set>
ProcFB: 0 xedrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.0.0-22-generic
root=UUID=95b909ce-2bd9-461b-88f7-b44bcb954f4b ro quiet splash
crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 06/05/2025
dmi.bios.release: 5.32
dmi.bios.vendor: American Megatrends International, LLC.
dmi.bios.version: UX5406SA.308
dmi.board.asset.tag: ATN12345678901234567
dmi.board.name: UX5406SA
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: 1.0
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: ASUSTeK COMPUTER INC.
dmi.chassis.version: 1.0
dmi.ec.firmware.release: 3.19
dmi.modalias:
dmi:bvnAmericanMegatrendsInternational,LLC.:bvrUX5406SA.308:bd06/05/2025:br5.32:efr3.19:svnASUSTeKCOMPUTERINC.:pnASUSZenbookS14UX5406SA_UX5406SA:pvr1.0:rvnASUSTeKCOMPUTERINC.:rnUX5406SA:rvr1.0:cvnASUSTeKCOMPUTERINC.:ct10:cvr1.0:sku:pfaASUSZenbookS14:
dmi.product.family: ASUS Zenbook S 14
dmi.product.name: ASUS Zenbook S 14 UX5406SA_UX5406SA
dmi.product.version: 1.0
dmi.sys.vendor: ASUSTeK COMPUTER INC.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute wayland-session
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https://bugs.launchpad.net/bugs/2156713
Title:
Core Ultra 7 258V (Lunar Lake) pinned to minimum frequency — BD
PROCHOT stuck asserted (ASUS Zenbook S14 UX5406SA)
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