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Message-ID: <ZmkCFyOXDC5KfC-5@google.com>
Date: Tue, 11 Jun 2024 19:04:07 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc: X86 Kernel <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Dave Hansen <dave.hansen@...el.com>, 
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	linux-perf-users@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>, 
	Andi Kleen <andi.kleen@...el.com>, Xin Li <xin3.li@...el.com>
Subject: Re:

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.

> 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.