linux-kernel - Re: [RFC PATCH v4 4/8] x86/apic: Introduce Remote Action Request Operations

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Message-ID: <mqeuxn4in7pscni5odii2qvzoils5ce3jdzvmp45w3bg462buj@4elenf2mxaro>
Date: Thu, 26 Jun 2025 16:20:37 +0300
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Rik van Riel <riel@...riel.com>
Cc: linux-kernel@...r.kernel.org, kernel-team@...a.com, 
	dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org, bp@...en8.de, 
	x86@...nel.org, nadav.amit@...il.com, seanjc@...gle.com, tglx@...utronix.de, 
	mingo@...nel.org, Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [RFC PATCH v4 4/8] x86/apic: Introduce Remote Action Request
 Operations

On Thu, Jun 19, 2025 at 04:03:56PM -0400, Rik van Riel wrote:
> From: Yu-cheng Yu <yu-cheng.yu@...el.com>
> 
> RAR TLB flushing is started by sending a command to the APIC.
> This patch adds Remote Action Request commands.
> 
> Because RAR_VECTOR is hardcoded at 0xe0, POSTED_MSI_NOTIFICATION_VECTOR
> has to be lowered to 0xdf, reducing the number of available vectors by
> 13.
> 
> [riel: refactor after 6 years of changes, lower POSTED_MSI_NOTIFICATION_VECTOR]

But why? Because it is used as FIRST_SYSTEM_VECTOR?

> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Signed-off-by: Rik van Riel <riel@...riel.com>
> ---
>  arch/x86/include/asm/apicdef.h     | 1 +
>  arch/x86/include/asm/irq_vectors.h | 7 ++++++-
>  arch/x86/include/asm/smp.h         | 1 +
>  arch/x86/kernel/apic/ipi.c         | 5 +++++
>  arch/x86/kernel/apic/local.h       | 3 +++
>  5 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/apicdef.h b/arch/x86/include/asm/apicdef.h
> index 094106b6a538..b152d45af91a 100644
> --- a/arch/x86/include/asm/apicdef.h
> +++ b/arch/x86/include/asm/apicdef.h
> @@ -92,6 +92,7 @@
>  #define		APIC_DM_LOWEST		0x00100
>  #define		APIC_DM_SMI		0x00200
>  #define		APIC_DM_REMRD		0x00300
> +#define		APIC_DM_RAR		0x00300

Hm. Do we conflict with APIC_DM_REMRD here?

>  #define		APIC_DM_NMI		0x00400
>  #define		APIC_DM_INIT		0x00500
>  #define		APIC_DM_STARTUP		0x00600

-- 
  Kiryl Shutsemau / Kirill A. Shutemov