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Subject: Re: [PATCH 00/31 v2] PTI support for x86_32
To: Pavel Machek <pavel@ucw.cz>, Andy Lutomirski <luto@kernel.org>
Cc: Joerg Roedel <joro@8bytes.org>, Thomas Gleixner <tglx@linutronix.de>,
 Ingo Molnar <mingo@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>,
 X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
 Linux-MM <linux-mm@kvack.org>, Linus Torvalds
 <torvalds@linux-foundation.org>, Dave Hansen <dave.hansen@intel.com>,
 Josh Poimboeuf <jpoimboe@redhat.com>, Juergen Gross <jgross@suse.com>,
 Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>,
 Jiri Kosina <jkosina@suse.cz>, Boris Ostrovsky <boris.ostrovsky@oracle.com>,
 Brian Gerst <brgerst@gmail.com>, David Laight <David.Laight@aculab.com>,
 Denys Vlasenko <dvlasenk@redhat.com>, Eduardo Valentin <eduval@amazon.com>,
 Greg KH <gregkh@linuxfoundation.org>, Will Deacon <will.deacon@arm.com>,
 "Liguori, Anthony" <aliguori@amazon.com>,
 Daniel Gruss <daniel.gruss@iaik.tugraz.at>, Hugh Dickins <hughd@google.com>,
 Kees Cook <keescook@google.com>, Andrea Arcangeli <aarcange@redhat.com>,
 Waiman Long <llong@redhat.com>, Joerg Roedel <jroedel@suse.de>
References: <1518168340-9392-1-git-send-email-joro@8bytes.org>
 <CALCETrUF61fqjXKG=kwf83JWpw=kgL16UvKowezDVwVA1=YVAw@mail.gmail.com>
 <20180209210918.GA7333@amd>
From: Andrew Cooper <andrew.cooper3@citrix.com>
Message-ID: <a5e37af1-cfa3-1284-cb1c-3912c30505e3@citrix.com>
Date: Fri, 9 Feb 2018 21:28:08 +0000
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On 09/02/2018 21:09, Pavel Machek wrote:
> On Fri 2018-02-09 17:47:43, Andy Lutomirski wrote:
>> PCID bit set in CPUID should print a big fat warning like "WARNING:
>> you are using 32-bit PTI on a 64-bit PCID-capable CPU.  Your
>> performance will increase dramatically if you switch to a 64-bit
>> kernel."
> Hardware supports PCID even on 32-bit kernels, no?

Attempting to set CR4.PCIDE is disallowed outside of long mode.  It is
strictly a 64bit-only feature.

~Andrew