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Date: Fri, 9 Feb 2018 20:11:12 +0100
From: Joerg Roedel <jroedel@suse.de>
Subject: Re: [PATCH 00/31 v2] PTI support for x86_32
Message-ID: <20180209191112.55zyjf4njum75brd@suse.de>
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To: 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>, Pavel Machek <pavel@ucw.cz>

Hi Andy,

On Fri, Feb 09, 2018 at 05:47:43PM +0000, Andy Lutomirski wrote:
> One thing worth noting is that performance of this whole series is
> going to be abysmal due to the complete lack of 32-bit PCID.  Maybe
> any kernel built with this option set that runs on a CPU that has the
> 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."

Thanks for your review. I can add this warning, but I just hope that not
a lot of people will actually see it :)


	Joerg

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