linux-kernel - Re: [PATCH v2 1/6] x86/irq: Add enumeration of NMI source reporting CPU feature

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Date: Tue, 11 Jun 2024 20:04:23 -0700
From: Xin Li <xin@...or.com>
To: "H. Peter Anvin" <hpa@...or.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>, X86 Kernel <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...el.com>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>, linux-perf-users@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>
Cc: Andi Kleen <andi.kleen@...el.com>, Xin Li <xin3.li@...el.com>
Subject: Re: [PATCH v2 1/6] x86/irq: Add enumeration of NMI source reporting
 CPU feature

On 6/11/2024 7:50 PM, H. Peter Anvin wrote:
> On June 11, 2024 7:32:54 PM PDT, Xin Li <xin@...or.com> wrote:
>> On 6/11/2024 9:54 AM, Jacob Pan wrote:
>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>>> index 1d7122a1883e..b8b15f20b94e 100644
>>> --- a/arch/x86/Kconfig
>>> +++ b/arch/x86/Kconfig
>>> @@ -511,12 +511,21 @@ config X86_CPU_RESCTRL
>>>    config X86_FRED
>>>    	bool "Flexible Return and Event Delivery"
>>>    	depends on X86_64
>>> +	select X86_NMI_SOURCE
>>>    	help
>>>    	  When enabled, try to use Flexible Return and Event Delivery
>>>    	  instead of the legacy SYSCALL/SYSENTER/IDT architecture for
>>>    	  ring transitions and exception/interrupt handling if the
>>>    	  system supports it.
>>>    +config X86_NMI_SOURCE
>>
>> Lets reuse X86_FRED instead of adding another hard config option. See
>> below.

<snip>

>>
>> With this, no need to add DISABLE_NMI_SOURCE to disabled-features.h:
>>
>> 1) If FRED is not available, NMI source won't be too.
>> 2) If FRED is available but not enabled, all features relying on FRED
>> should be cleared. We probably should move the feature bits clearing
>> code into a static function when more such features are added in future.
>>
>>>      	/* Init cpu_entry_area before IST entries are set up */
>>>    	setup_cpu_entry_areas();
>>
>> Thanks!
>>     Xin
> 
> And even if we did, FRED should not *select* NMI_SOURCE; the dependency goes the other way.

Right, I was a bit of confused but was focusing on why do we need this.