linux-kernel - Re: [PATCH v1 13/26] x86/cpuid: Scan CPUID(0x2)

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Message-ID: <aBnFRrnZQ9HwwULK@gmail.com>
Date: Tue, 6 May 2025 10:16:06 +0200
From: Ingo Molnar <mingo@...nel.org>
To: "Ahmed S. Darwish" <darwi@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	John Ogness <john.ogness@...utronix.de>, x86@...nel.org,
	x86-cpuid@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 13/26] x86/cpuid: Scan CPUID(0x2)


* Ahmed S. Darwish <darwi@...utronix.de> wrote:

> +static void cpuid_read_0x2(const struct cpuid_scan_entry *e, struct cpuid_read_output *output)
> +{
> +	union leaf_0x2_regs *regs = (union leaf_0x2_regs *)output->leaf;
> +	struct leaf_0x2_0 *l2 = (struct leaf_0x2_0 *)output->leaf;
> +	int invalid_regs = 0;
> +
> +	/*
> +	 * All Intel CPUs must report an iteration count of 1.	In case of
> +	 * bogus hardware, keep the leaf marked as invalid at the CPUID table.
> +	 */
> +	cpuid_subleaf(e->leaf, e->subleaf, l2);
> +	if (l2->iteration_count != 0x01)
> +		return;
> +
> +	/*
> +	 * The most significant bit (MSB) of each register must be clear.
> +	 * If a register is malformed, replace its descriptors with NULL.
> +	 */
> +	for (int i = 0; i < 4; i++) {
> +		if (regs->reg[i].invalid) {
> +			regs->regv[i] = 0;
> +			invalid_regs++;
> +		}

Could we please emit a one-time syslog warning & diagnostic when we run 
across invalid or otherwise weird looking CPUID data, instead of just 
silently skipping and sanitizing it?

Thanks,

	Ingo