linux-kernel - Re: [patch v5 01/19] x86/cpu: Provide cpuid

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Date: Wed, 24 Jan 2024 21:02:07 +0100
From: Borislav Petkov <bp@...en8.de>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	Tom Lendacky <thomas.lendacky@....com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Huang Rui <ray.huang@....com>, Juergen Gross <jgross@...e.com>,
	Dimitri Sivanich <dimitri.sivanich@....com>,
	Sohil Mehta <sohil.mehta@...el.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Zhang Rui <rui.zhang@...el.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Feng Tang <feng.tang@...el.com>,
	Andy Shevchenko <andy@...radead.org>,
	Michael Kelley <mhklinux@...look.com>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch v5 01/19] x86/cpu: Provide cpuid_read() et al.

On Wed, Jan 24, 2024 at 01:25:12PM +0100, Borislav Petkov wrote:
> > +static inline void __cpuid_read_reg(unsigned int leaf, unsigned int subleaf,
> > +				    enum cpuid_regs_idx regidx, u32 *reg)
> > +{
> > +	u32 regs[4];
> > +
> > +	__cpuid_read(leaf, subleaf, regs);
> > +	*reg = regs[regidx];
> 
> Why not do
> 
> 	return regs[regidx];
> 
> instead?

Or do you really want to be able to use anonymous structs with bitfields
in them and then convert them to a u32 * when passing in to
cpuid_leaf_reg() etc in order to save yourself all the masking and
shifting and read out the bitfields directly?

I'm looking at the parse_topology() use case.

Looks like it...

-- 
Regards/Gruss,
    Boris.

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