linux-kernel - Re: [PATCH v9 03/18] x86/apic: Populate .read()/.write() callbacks of Secure AVIC driver

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Message-ID: <20250819143214.GKaKSK7rABhHAldbbR@fat_crate.local>
Date: Tue, 19 Aug 2025 16:32:14 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Upadhyay, Neeraj" <neeraj.upadhyay@....com>
Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	dave.hansen@...ux.intel.com, Thomas.Lendacky@....com,
	nikunj@....com, Santosh.Shukla@....com, Vasant.Hegde@....com,
	Suravee.Suthikulpanit@....com, David.Kaplan@....com, x86@...nel.org,
	hpa@...or.com, peterz@...radead.org, seanjc@...gle.com,
	pbonzini@...hat.com, kvm@...r.kernel.org,
	kirill.shutemov@...ux.intel.com, huibo.wang@....com,
	naveen.rao@....com, francescolavra.fl@...il.com,
	tiala@...rosoft.com
Subject: Re: [PATCH v9 03/18] x86/apic: Populate .read()/.write() callbacks
 of Secure AVIC driver

On Tue, Aug 19, 2025 at 09:45:02AM +0530, Upadhyay, Neeraj wrote:
> Maybe change it to below?
> 
> /*
>  * Valid APIC_IRR/SAVIC_ALLOWED_IRR registers are at 16 bytes strides
>  * from their respective base offset.
>  */
> 
> if (WARN_ONCE(!(IS_ALIGNED(reg - APIC_IRR, 16) ||
>                 IS_ALIGNED(reg - SAVIC_ALLOWED_IRR, 16)),
>               "Misaligned APIC_IRR/ALLOWED_IRR APIC register read offset
> 0x%x",
>               reg))

Let's beef that up some more with a crystal-clear explanation what is going on
here so that readers don't have to stop and stare for 5 mins before they grok
what this is doing:

	/*
	 * Valid APIC_IRR/SAVIC_ALLOWED_IRR registers are at 16 bytes strides from
	 * their respective base offset. APIC_IRRs are in the range
	 *
	 * (0x200, 0x210,  ..., 0x270)
	 *
	 * while the SAVIC_ALLOWED_IRR range starts 4 bytes later, in the rangea
	 * 
	 * (0x204, 0x214, ..., 0x274).
	 *
	 * Filter out everything else.
	 */
	 if (WARN_ONCE(!(IS_ALIGNED(reg, 16) ||
		 	 IS_ALIGNED(reg - 4, 16)),
		      "Misaligned APIC_IRR/ALLOWED_IRR APIC register read offset 0x%x", reg));

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette