ACK: [PATCH 0/1] [Noble][AWS] support Out-Of-Band pstate mode for Emerald Rapids

[Cengiz Can]

On 12-09-24 15:51:43, Philip Cox wrote:
> 
> BugLink: https://bugs.launchpad.net/bugs/2080569
> 
> 
> 
> SRU Justification:
> 
> [Impact]
> 
> In Emerald Rapids VMs, a stack trace is printed during boot on 6.8 based kernels, but not 6.5 ones. 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]
> 
> The reason that these traces are not found in the 6.5 kernel, but are in the 6.8 kernel one had the traces is that in the 6.5 kernel the CPU in the instance (Emerald Rapids) does not have the pstate support added yet. The 6.8 kernel does have support though. That is why they don't appear in the 6.5 kernel, but in the 6.8 kernel.
> 
> In the 6.11 kernel the patch https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7e1c3f584ee78b0d0210fc424420d9529f3ca952 was added to prevent trying to set the p-states while in OOB (Out-of-band) mode. So, rather than having the VM trying to set the p-states, it is handled by the host OS/platform.
> 
> [Test Plan]
> 
> I have tested this.
> 
> [Where problems could occur]
> In the 6.11 kernel tree where this change comes from, there has been some significant refactoring of the code. If other changes need to be back-ported to the AWS 6.8 kernel, other conflicts or issues may arise.
> 
> [Other]
> SF #00395865
> 
> 
> --
> 
> Srinivas Pandruvada (1):
>   cpufreq: intel_pstate: Support Emerald Rapids OOB mode

Acked-by: Cengiz Can <cengiz.can at canonical.com>

> 
>  drivers/cpufreq/intel_pstate.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> -- 
> 2.34.1
> 
> 
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