Patch submitted: https://lists.ubuntu.com/archives/kernel-
team/2024-October/154680.html
** Changed in: linux (Ubuntu Noble)
Status: New => In Progress
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https://bugs.launchpad.net/bugs/2084834
Title:
[SRU] cpufreq: intel_pstate: Support Emerald Rapids OOB mode
Status in linux package in Ubuntu:
New
Status in linux source package in Noble:
In Progress
Bug description:
This is a public version of: https://bugs.launchpad.net/bugs/2078894
[Impact]
In Emerald Rapids VMs with OOB P-states enabled, a stack trace is
printed during boot on 6.8 based kernels. The stack traces look like:
[ 1.206658] intel_pstate: Intel P-state driver initializing
[ 1.207453] unchecked MSR access error: WRMSR to 0x199 (tried to write
0x0000000000000800) at rIP: 0xffffffffb94c3b24 (native_write_msr+0x4/0x40)
[ 1.208422] Call Trace:
[ 1.208422] <TASK>
[ 1.208422] ? show_stack_regs+0x23/0x40
[ 1.208422] ? ex_handler_msr+0x10a/0x180
[ 1.208422] ? fixup_exception+0x183/0x390
[ 1.208422] ? gp_try_fixup_and_notify+0x23/0xc0
[ 1.208422] ? exc_general_protection+0x15e/0x480
[ 1.208422] ? asm_exc_general_protection+0x27/0x30
[ 1.208422] ? __pfx___wrmsr_on_cpu+0x10/0x10
[ 1.208422] ? native_write_msr+0x4/0x40
[ 1.208422] ? __wrmsr_on_cpu+0x4b/0x90
[ 1.208422] ? __pfx___rdmsr_on_cpu+0x10/0x10
[ 1.208422] ? __pfx___wrmsr_on_cpu+0x10/0x10
[ 1.208422] generic_exec_single+0x7e/0x120
[ 1.208422] smp_call_function_single+0x103/0x140
[ 1.208422] ? __pfx___wrmsr_on_cpu+0x10/0x10
[ 1.208422] wrmsrl_on_cpu+0x57/0x80
[ 1.208422] intel_pstate_set_pstate+0x3e/0x80
[ 1.208422] intel_pstate_get_cpu_pstates.constprop.0+0xd7/0x190
[ 1.208422] intel_pstate_init_cpu+0x3f/0x140
[ 1.208422] intel_cpufreq_cpu_init+0x44/0x270
[ 1.208422] ? freq_qos_add_notifier+0x45/0x80
[ 1.208422] cpufreq_online+0x444/0xb80
[ 1.208422] cpufreq_add_dev+0x99/0xd0
[ 1.208422] subsys_interface_register+0x11c/0x140
[ 1.208422] cpufreq_register_driver+0x1b5/0x330
[ 1.208422] intel_pstate_register_driver+0x48/0xd0
[ 1.208422] intel_pstate_init+0x25c/0x810
[ 1.208422] ? __pfx_intel_pstate_init+0x10/0x10
[ 1.208422] do_one_initcall+0x5b/0x310
[ 1.208422] do_initcalls+0x104/0x210
[ 1.208422] ? __pfx_kernel_init+0x10/0x10
[ 1.208422] kernel_init_freeable+0x134/0x1f0
[ 1.208422] kernel_init+0x1b/0x200
[ 1.208422] ret_from_fork+0x44/0x70
[ 1.208422] ? __pfx_kernel_init+0x10/0x10
[ 1.208422] ret_from_fork_asm+0x1b/0x30
[ 1.208422] </TASK>
[Fix]
Cherry pick of 7e1c3f584ee7 - cpufreq: intel_pstate: Support Emerald Rapids
OOB mode
Upstream since v6.11.
Very simple change as the OOB identifying bits are same as for the prior
generation CPUs like Sapphire Rapids servers, so also add Emerald Rapids to
the
intel_pstate_cpu_oob_ids[] list.
[Test Plan]
Set HW PM OOB mode in BIOS power management config.
Make sure that no cpufreq drivers are loaded. You can verify that
/sys/devices/system/cpu/cpu0/cpufreq/scaling_driver is not present or any
cpufreq interface.
It's also already part of linux-aws:
https://bugs.launchpad.net/bugs/2078894
[Where problems could occur]
cpufreq regression.
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