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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 9 Feb 2018 13:11:52 -0800
Message-ID: <CA+55aFy7sme11ok4FqZD2upvF+4g3sDK-yQakNnD1LAsALDOUQ@mail.gmail.com>
Subject: Re: [PATCH 00/31 v2] PTI support for x86_32
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Sender: owner-linux-mm@kvack.org
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To: Pavel Machek <pavel@ucw.cz>
Cc: Andy Lutomirski <luto@kernel.org>, 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>, 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>

On Fri, Feb 9, 2018 at 1:09 PM, Pavel Machek <pavel@ucw.cz> wrote:
>
> Hardware supports PCID even on 32-bit kernels, no?

We're not adding support for it even if it were possible. No way.

Christ, even if you want to run 32-bit user code, you'd better run a
64-bit kernel. Backporting the PCID bits to something that no actual
real developer will ever use is crazy and unacceptable.

             Linus

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