ACK: [SRU][N][PATCH 0/1] cpufreq: intel_pstate: Support Emerald Rapids OOB mode

[ivanhu]

Acked-by: Ivan Hu <ivan.hu at canonical.com>

On 2024/10/18 04:37, Thibault Ferrante wrote:
> BugLink: https://bugs.launchpad.net/bugs/2084834
> 
> [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.
> 
> Srinivas Pandruvada (1):
>    cpufreq: intel_pstate: Support Emerald Rapids OOB mode
> 
>   drivers/cpufreq/intel_pstate.c | 1 +
>   1 file changed, 1 insertion(+)
>