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Message-ID: <20180714050828.wl44vgwa7kzptsws@suse.de>
Date: Sat, 14 Jul 2018 07:08:28 +0200
From: Joerg Roedel <jroedel@...e.de>
To: Andy Lutomirski <luto@...nel.org>
Cc: Joerg Roedel <joro@...tes.org>, Borislav Petkov <bp@...en8.de>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...nel.org>,
"H . Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Dave Hansen <dave.hansen@...el.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Juergen Gross <jgross@...e.com>,
Peter Zijlstra <peterz@...radead.org>,
Jiri Kosina <jkosina@...e.cz>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Brian Gerst <brgerst@...il.com>,
David Laight <David.Laight@...lab.com>,
Denys Vlasenko <dvlasenk@...hat.com>,
Eduardo Valentin <eduval@...zon.com>,
Greg KH <gregkh@...uxfoundation.org>,
Will Deacon <will.deacon@....com>,
"Liguori, Anthony" <aliguori@...zon.com>,
Daniel Gruss <daniel.gruss@...k.tugraz.at>,
Hugh Dickins <hughd@...gle.com>,
Kees Cook <keescook@...gle.com>,
Andrea Arcangeli <aarcange@...hat.com>,
Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
"David H . Gutteridge" <dhgutteridge@...patico.ca>
Subject: Re: [PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID
capable CPU
On Fri, Jul 13, 2018 at 11:59:44AM -0700, Andy Lutomirski wrote:
> On Wed, Jul 11, 2018 at 4:29 AM, Joerg Roedel <joro@...tes.org> wrote:
> > From: Joerg Roedel <jroedel@...e.de>
> >
> > Warn the user in case the performance can be significantly
> > improved by switching to a 64-bit kernel.
>
> ...
>
> > +#ifdef CONFIG_X86_32
> > + if (boot_cpu_has(X86_FEATURE_PCID)) {
>
> I'm a bit confused. Wouldn't the setup_clear_cpu_cap() call in
> early_identify_cpu() prevent this from working?
Right you are, I don't have a PCID capable system at hand for testing,
so I didn't catch this...
> Boris, do we have a straightforward way to ask "does the CPU advertise
> this feature in CPUID regardless of whether we have it enabled right
> now"?
I guess we need to call cpuid again.
Regards,
Joerg
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