linux-kernel - Re: [PATCH v7 08/10] x86/nmi: Enable NMI-source for IPIs delivered as NMIs

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Message-ID: <768d8534-454e-4c3d-a41e-3f82c2347b0e@intel.com>
Date: Thu, 24 Jul 2025 15:59:12 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: Thomas Gleixner <tglx@...utronix.de>, Dave Hansen
	<dave.hansen@...ux.intel.com>
CC: "H . Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>, "Ingo
 Molnar" <mingo@...hat.com>, <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	Xin Li <xin@...or.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra
	<peterz@...radead.org>, Adrian Hunter <adrian.hunter@...el.com>, Kan Liang
	<kan.liang@...ux.intel.com>, Tony Luck <tony.luck@...el.com>, Zhang Rui
	<rui.zhang@...el.com>, Steven Rostedt <rostedt@...dmis.org>, Andrew Cooper
	<andrew.cooper3@...rix.com>, "Kirill A . Shutemov"
	<kirill.shutemov@...ux.intel.com>, Jacob Pan <jacob.pan@...ux.microsoft.com>,
	Andi Kleen <ak@...ux.intel.com>, Kai Huang <kai.huang@...el.com>, "Sandipan
 Das" <sandipan.das@....com>, <linux-perf-users@...r.kernel.org>,
	<linux-edac@...r.kernel.org>, <kvm@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>, "Sean
 Christopherson" <seanjc@...gle.com>
Subject: Re: [PATCH v7 08/10] x86/nmi: Enable NMI-source for IPIs delivered as
 NMIs

Hi Thomas, Dave,

Seeking your inputs on the below direction.

On 7/10/2025 3:40 PM, Sean Christopherson wrote:
>>> One thought would be to pass a small struct (by value), and then provide macros
>>> to generate the structure for a specific vector.  That provides some amount of
>>> type safety and should make it a bit harder to pass in garbage, without making
>>> the callers any less readable.
>>>
>>> struct apic_ipi {
>>> 	u8 vector;
>>> 	u8 type;
>>> };
>>>  
>>> #define APIC_IPI(v, t) ({ struct apic_ipi i = { .vector = v, .type = t }; i; })
>>> #define APIC_IPI_IRQ(vector) APIC_IPI(vector, APIC_DELIVERY_MODE_FIXED)
>>> #define APIC_IPI_NMI(vector) APIC_IPI(vector, APIC_DELIVERY_MODE_NMI)
>>> 
>>> #define IPI_IRQ_WORK		APIC_IPI_IRQ(IRQ_WORK_VECTOR)
>>> #define IPI_POSTED_INTR_WAKEUP	APIC_IPI_IRQ(POSTED_INTR_WAKEUP_VECTOR)
>>> 
>>> #define IPI_NMI_BACKTRACE	APIC_IPI_NMI(NMI_BACKTRACE_VECTOR)
>>> 
>>> static __always_inline void __apic_send_IPI_self(struct apic_ipi ipi)
>>
>> I am fine with this approach. Though, the changes would be massive since
>> we have quite a few interfaces and a lot of "struct apic".
> 
> It'd definitely be big, but it doesn't seem like it'd be overwhelmingly painful.
> Though it's certainly enough churn that I wouldn't do anything until there's a
> consensus one way or the other :-)
> 

In order to accommodate NMI source vectors, updating the send_IPI_*()
APIs seems like the right thing to do for the long run. But it would
introduce some churn. Is this the optimal path forward? Any other
options we should consider?