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Message-ID: <41287f0c-4c1c-472b-a6ef-5669c68aad76@zytor.com>
Date: Tue, 11 Jun 2024 19:55:30 -0700
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Subject: Re:
To: Sean Christopherson <seanjc@google.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: X86 Kernel <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Dave Hansen <dave.hansen@intel.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        linux-perf-users@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Andi Kleen <andi.kleen@intel.com>, Xin Li <xin3.li@intel.com>
References: <20240611165457.156364-1-jacob.jun.pan@linux.intel.com>
 <ZmkCFyOXDC5KfC-5@google.com>
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From: Xin Li <xin@zytor.com>
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On 6/11/2024 7:04 PM, Sean Christopherson wrote:
> On Tue, Jun 11, 2024, Jacob Pan wrote:
>> To tackle these challenges, Intel introduced NMI source reporting as a part
>> of the FRED specification (detailed in Chapter 9).
> 
> Chapter 9 of the linked spec is "VMX Interactions with FRED Transitions".  I
> spent a minute or so poking around the spec and didn't find anything that describes
> how "NMI source reporting" works.

I did the same thing when I saw NMI source was added to the spec :)

> 
>> 1.	Performance monitoring.
>> 2.	Inter-Processor Interrupts (IPIs) for functions like CPU backtrace,
>> 	machine check, Kernel GNU Debugger (KGDB), reboot, panic stop, and
>> 	self-test.
>>
>> Other NMI sources will continue to be handled as previously when the NMI
>> source is not utilized or remains unidentified.
>>
>> Next steps:
>> 1. KVM support
> 
> I can't tell for sure since I can't find the relevant spec info, but doesn't KVM
> support need to land before this gets enabled?  Otherwise the source would get
> lost if the NMI arrived while the CPU was in non-root mode, no?  E.g. I don't
> see any changes to fred_entry_from_kvm() in this series.

You're absolutely right!

There is a patch in NMI source KVM patches for this, but as you
mentioned it has to be in this NMI source native patches instead.

Thanks!
     Xin