From mboxrd@z Thu Jan  1 00:00:00 1970
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Subject: Re: [RESEND PATCH 1/3] x86: Adding structs to reflect cpuid fields
Date: Thu, 18 Sep 2014 12:00:17 +0200
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Cc: Nadav Amit <namit@cs.technion.ac.il>,
	Ingo Molnar <mingo@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	the arch/x86 maintainers <x86@kernel.org>,
	kvm <kvm@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Borislav Petkov <bp@alien8.de>
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2014-09-18 09:19+0200, Borislav Petkov:
> On Thu, Sep 18, 2014 at 02:29:54AM +0200, Radim Kr=C4=8Dm=C3=A1=C5=99=
 wrote:
> > I think you proposed to use magic constant in place of of MASK_FAM_=
X, so
>=20
> Huh, what?

Your example.  It cannot be verbatim MASK_FAM_X in real code.

I interpreted it to be a placeholder for 0x1ffff (first 17 bits) and
said why I think it is not a good thing.
The other interpretation (well named macro) was against your goal.

> > Second problem:  Most elements don't begin at offset 0, so the usua=
l
> > retrieval would add a shift, (repurposing max_monitor_line_size)
>=20
> So what?

Your goal was easy parsing (last sentence of the mail).

My argument is that bitfields are easier to read.  (With examples.)

> >  max_monitor_line_size =3D (cpuid & MASK_FAM_X) >> OFFSET_FAM_X;
> >=20
> > and it's not better when we write it back after doing stuff.
>=20
> Writing back CPUID on baremetal? You can't be serious.

We are not talking just about baremetal, see patch [3/3].

There are, and will be new, use cases for modifying and storing cpuid.

> Ok, this is getting ridiculous so I'll stop wasting time. I stand by =
my
> initial statement - this is a bad idea.

Acknowledged.