linux-kernel - Re: [RFC v2 13/17] x86/apic: Handle EOI writes for SAVIC guests

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Message-ID: <87cyea2xxi.ffs@tglx>
Date: Fri, 21 Mar 2025 16:41:45 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Neeraj Upadhyay <Neeraj.Upadhyay@....com>, linux-kernel@...r.kernel.org
Cc: bp@...en8.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
Subject: Re: [RFC v2 13/17] x86/apic: Handle EOI writes for SAVIC guests

On Wed, Feb 26 2025 at 14:35, Neeraj Upadhyay wrote:
> +static int find_highest_isr(void *backing_page)
> +{
> +	int vec_per_reg = 32;
> +	int max_vec = 256;
> +	u32 reg;
> +	int vec;
> +
> +	for (vec = max_vec - 32; vec >= 0; vec -= vec_per_reg) {
> +		reg = get_reg(backing_page, APIC_ISR + REG_POS(vec));
> +		if (reg)
> +			return __fls(reg) + vec;
> +	}
> +
> +	return -1;

Congrats. You managed to re-implement find_last_bit() in the most
incomprehesible way.

Thanks,

        tglx