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From: Thomas Gleixner <tglx@linutronix.de>
To: Borislav Petkov <bp@alien8.de>
Cc: LKML <linux-kernel@vger.kernel.org>, x86@kernel.org, Tom Lendacky
 <thomas.lendacky@amd.com>, Andrew Cooper <andrew.cooper3@citrix.com>,
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 <dimitri.sivanich@hpe.com>, Sohil Mehta <sohil.mehta@intel.com>, K Prateek
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 Zhang Rui <rui.zhang@intel.com>, "Paul E. McKenney" <paulmck@kernel.org>,
 Feng Tang <feng.tang@intel.com>, Andy Shevchenko <andy@infradead.org>,
 Michael Kelley <mhklinux@outlook.com>, "Peter Zijlstra (Intel)"
 <peterz@infradead.org>
Subject: Re: [patch v5 06/19] x86/cpu: Provide a sane leaf 0xb/0x1f parser
In-Reply-To: <20240130193102.GEZblOdor_bzoVhT0f@fat_crate.local>
References: <20240117115752.863482697@linutronix.de>
 <20240117115908.674834306@linutronix.de>
 <20240130193102.GEZblOdor_bzoVhT0f@fat_crate.local>
Date: Mon, 12 Feb 2024 15:17:45 +0100
Message-ID: <87il2tlqba.ffs@tglx>
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On Tue, Jan 30 2024 at 20:31, Borislav Petkov wrote:
> On Tue, Jan 23, 2024 at 01:53:39PM +0100, Thomas Gleixner wrote:
>> +static inline bool topo_subleaf(struct topo_scan *tscan, u32 leaf, u32 subleaf,
>
> "parse_topo_subleaf"?
>
> With a verb in the name...
>
>> +				unsigned int *last_dom)
>> +{
>> +	unsigned int dom, maxtype;
>> +	const unsigned int *map;
>> +	struct {
>> +		// eax
>
> Can we please not use those yucky // comments together with the
> multiline ones?

TBH, the // comment style is really better for struct definitions. It's
denser and easier to parse.

		// eax
		u32	x2apic_shift	:  5, // Number of bits to shift APIC ID right
					      // for the topology ID at the next level
					: 27; // Reserved
		// ebx
		u32	num_processors	: 16, // Number of processors at current level
					: 16; // Reserved

versus:

		/* eax */
		u32	x2apic_shift	:  5, /*
                                               * Number of bits to shift APIC ID right
					       * for the topology ID at	the next level
                                               */
					: 27; /* Reserved */

		/* ebx */
		u32	num_processors	: 16, /* Number of processors at current level */
					: 16; /* Reserved */

Especially x2apic_shift is horrible and the comments of EBX are visually
impaired while with the C++ comments x2apic_shift looks natural and the
EBX comments are just open to the right and therefore simpler.

>> +	if (!tscan->dom_shifts[TOPO_SMT_DOMAIN] && tscan->dom_ncpus[TOPO_SMT_DOMAIN] > 1) {
>> +		unsigned int sft = get_count_order(tscan->dom_ncpus[TOPO_SMT_DOMAIN]);
>> +
>> +		pr_warn_once(FW_BUG "CPUID leaf 0x%x subleaf 0 has shift level 0 but %u CPUs\n",
>> +			     leaf, tscan->dom_ncpus[TOPO_SMT_DOMAIN]);
>
> Do you really wanna warn about that? Hoping that someone would do
> something about it while there's time...?

If it's caught in early testing, this should be fixed, no?

Thanks,

        tglx