linux-kernel - Re: [PATCH] MIPS: mm: tlb-r4k: Uniquify TLB entries on init

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Message-ID: <alpine.DEB.2.21.2506070300430.1790@angie.orcam.me.uk>
Date: Sat, 7 Jun 2025 03:48:15 +0100 (BST)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Jiaxun Yang <jiaxun.yang@...goat.com>
cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>, 
    linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: mm: tlb-r4k: Uniquify TLB entries on init

On Thu, 5 Jun 2025, Jiaxun Yang wrote:

> +static unsigned long r4k_safe_entryhi(void)
> +{
> +	int entry = current_cpu_data.tlbsize;
> +	int old_index;
> +
> +	old_index = read_c0_index();
> +	while (entry >= 0) {
[...]
> +		entry++;
> +	}

 Hmm, how is it supposed to work: you start from say 48 and then iterate 
until 0x80000000 before giving up?  Also a signed overflow condition is UB 
pre-C23, so the compiler may well optimise the loop control away.

 How did you verify this code?

  Maciej